I like the look of these, but they're so expensive! I've had the an almost identically designed chair from Focus DIY (iirc) for 4 years now, was half the price.
Admittedly, It's looking a bit sorry for itself after years of abuse and I'm on the lookout for a replacement. Just can't bring myself to drop over a ton on a computer chair.
I hesitated too. I happened to get lucky with a £50 chair from Staples a few years ago. It was comfortable and it had a genuinely high back. i.e. higher than my head when I was sitting in it. But it was made of plastic and the back was held to the seat by the arms. One of which, inevitably, snapped. The seat had become a little bent as well, so it was lower at the front than at the back. Maybe due to me sitting too far forward, maybe due to the extra force on it in that direction when the chair was tilted. But I got a good 3 years use from it, so it was a bargain.
Then I ignored the recommendations for Markus and bought a £60 chair from a company we're not allowed to mention here. High back, metal frame and arms, lumbar support. Much better...no. As usual, the term 'high back' was misleading. 'high' is a completely meaningless word in this context because no comparison is given. So I paid £60 for a chair suitable for someone 6 inches shorter than me. The 'high back' just about reached my shoulders and the lumbar support for your neck started halfway down my back, pushing my head forward uncomfortably.
So I did what I should have done in the first place and bought a Markus. It's so superior to that new £60 chair that a comparison is amusing. It's made me realise that the old chair I had from Staples, the one that I considered comfortable, was in fact merely adequate. I spent 14 hours in it the first day I got it - 6 hours sitting followed by 8 hours sleeping. No problem. It was as good as a decent bed. It's surprising how much difference is made by the seat tilting far less than the back rather than both tilting together as they do in cheap chairs.
To the OP:
If you sit in the chair for more than a trivial amount of time, the extra £50 or so for a Markus is money well spent. I would suggest sitting in it first if it isn't too inconvenient for you to go to an Ikea. It's always a good idea to sit in a chair before deciding whether or not to buy it.
If you're really limited to £50 or so, I suggest trying the new model high back mesh chair from Ryman. I sat in the old model high back mesh chair, which was comfortable but didn't have a genuinely high back. The new one looks like it would be high enough to support my head (I'm 5'11").