Having owned both chairs recently, here are my thoughts starting from the ground up.
Both chairs are supplied with the exact same casters and chair lift in the box, they are clearly from the same supplier. However Noblechair is the only company to offer optional after-market purchases to further optimise your chair to fit your preferences, including hard-wood floor casters and shorter/longer chair lifts. But I think most importantly, especially going into the future and because accidents happen, Noblechair seem to better stocked when it comes to spares to repair your chair. Secretlab's chair parts on their store has been out of stock for as long as I can remember, which does not bode well.
Now the wheel base. There are differences in design, but structurally both seem to do the job. Secretlab wheelbase is finished with a gloss black paint, which is quite fragile and even with minor bumps it was chipping. In fact the wheelbase I received was already a casualty of this. Noblechair on the other hand have black powder coated their wheelbase, which is very tough! Even my little dog can't leave a scratch on it.
The same multi-directional tilt mechanism is supplied to both chairs. They do the same job in the same way.
Now the armrests. Both are coated in a cold-injection foam but with slight design differences. Secretlab's foam is softer and has a slight concave surface, which offers a little more grip than Noblechair's design. But that being said I've had no issues of sliding around on the Noblechair design, but the softer foam was a nice touch. Both armrests have 4 way adjust, because they are (surprise surprise) based on the exact same design. Secretlab's buttons/switches for adjusting the armrests are more accessible on the fly, whereas with Noblechair you do have to feel around for them. However as a chronic fidgeter, having the switches tucked away isn't necessarily a bad thing in my case.
Now for the chair. Both companies are clearly using the exact same chair frame but with slightly different designs and styling, that is why really there is very little difference between the two chairs. So to confirm most of the questions asked in this thread, both chairs are using the exact same lumbar support feature. Noblechair is not giving vertical adjustment, they are both exactly the same. Where they differ is the padding, structural reinforcement and final styling. Starting with padding, Secretlab is made with a slightly softer foam, which is noticed especially in the seat base, but that isn't to say that the Noblechair feels like sitting on a rock, because they are both very comfortable to sit on long hours. However Noblechair does seem to offer more support with their choice of foam padding and I would hazard a guess (without ripping the chair open) more structural reinforcement, which would probably explain the larger weight limit. Here's an example; with the Secretlab chair the front of the seat base was being almost completely compressed (where your legs overhang), like there was no support or resistance in the foam to the point I could almost feel the frame of the chair (and I am no where near the 130kg weight limit). You could even see it in the way the PU leather was forming a crease at the front of the chair as it was folding over where the foam behind it was being compressed. This was noticed from day one. So far the Noblechair has not done this, it feels comfortable and strong. I can compare the difference between the two like how laying down to sleep on a pile of downy pillows might feel luxurious but your back won't love you in the morning. But that being said I find both chairs very comfortable to sit on for long hours. Secretlab shouldn't give you back problems for being softer, and Noblechair shouldn't cause soreness. I just think in this case Noblechair have gotten the balance between support and comfort tuned better than Secretlab.
One other example comes to mind now; because Secretlab use a softer foam with less compression resistance in the backrest too, I found that you can feel the lumbar support mechanism pushing into your back through the foam. This was not as uncomfortable as it sounds, it was something I was aware of but not particularly bothered by, though a couple of friends and a relative who tried the chair disagreed with me. With the Noblechair I have tried the lumbar support dialled up to the max and still cannot feel this sensation, and as you adjust the support while sitting in the chair it feels like a greater surface area is affected by adjusting the mechanism, rather than a small surface area like I felt with the Secretlab chair. Again neither chair offer a poor design, but I do think Noblechair have made better use of this feature with their design.
As for their optional extras, both chairs come with an optional neck/head pillow. Secretlab is easily the nicer one with its soft memory foam filling, whereas the Noblechair one feels like its filled with scraps from the silent-night factory, which I am going to replace with an aftermarket purchase. Noblechair also include an optional lumbar pillow, which Secretlab does not, but honestly I don't think either chair needs it unless your back has a right angle.
I've been as critical as possible because both chairs are based on the same frame design and are almost identical, especially now that Secretlab have dropped their prices to compete with Noblechair. So its really a judgement call as to what style you prefer. I preferred the style of the Noblechair Hero, which is why I returned the Secretlab Titan (stealth) after owning it for nearly two weeks just as the Hero was announced. I made the swap without being assured that I would end up preferring the overall design of the Noblechair, so obviously I am glad I did choose Noblechair over Secretlab. It seems to me like Noblechair as the late comer have taken ideas from Secretlab's consumer feedback and used that to make a slightly superior chair, from what is already a very comfortable chair. I guess my advise is that you cannot go wrong with either product, go with what you appeals to you and I hope my direct comparison might help anyone sitting on the fence.
Just one final point though (I don't want to be that guy who whines about their experience, but I feel some warning is due). Secretlab's customer service for the UK is terrible. Their customer service support centre is based in Singapore, they have no European office. So should you have a problem expect to exchange one email a day (as they are +8 GMT). Should you need to send anything back it has to go to a client fulfilment centre (not owned by Secretlab) who then have to inspect and liaise with Secretlab in the same way the customer does. In short it took 3 weeks for the return on my Titan to be finalised. On the other hand I've never had an issue with a product bought though Overclockers which could not be solved in a 10 minute phone call the same day. And returns are generally sorted next day (not including weekends).
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