Our experiences with the 190 differ somewhat. I found it extremely susceptible to the slightest vibration. Usable, just, at low height but truly dreadful fully extended.
It was my first tripod used with a modest 30D and 70-300 f/4-5.6. Relegated it to reflector holder duty.
Cheap tripods can be good if you don't mind weight. I like weight so ended up with Uniloc Major. The good thing about cheap heavy tripods is they're even cheaper when the muscularly disadvantaged sell them on.
When you say fully extended do you mean with the centre column extended too? I actually removed the centre column on mine, and I also have the carbon version - carbon makes a fairly significant difference with high frequency vibrations. There are very few vibrations to be seen. I'm sure it's not as stable as something like a 055 or Gitzo equivalent, but they are just to big for most situations and you don't need the extra stability the vast majority of the time. If the Op was thinking about sticking a 600 f/4 on it then I'd probably have a different recommendation. That said you really shouldn't have an issue with a good head and the centre column down/removed/tight with a 70-300.
Not in my experience, the small light cheap tripods just don't cut it and you end up with soft photos. With a monopod you are already committing to using suitable shutter speeds and it helps stabilize things a lot, removing the high-frequency movements which is what robs sharpness. Furthermore, the degrees of freedom relate to rotations which the optical stabilization does a very good job of eliminating. For heavy lenses it is useful to have something take the weight.
Cheap is a relative term. The 190CX and Mefoto Roadtrip (carbon version as well) aren't "cheap". I tested out one of the Gitzo travellers when looking to buy the Mefoto and there was very little in it. There's a world of difference between them and the £50-100 cheap/light tripods you may be discussing. It's also worth pointing out the OP is not using a D5 with a fast long prime, he's looking for something sturdy to put a mirrorless on.
I agree, for heavy lenses something to rest it on helps, but I find I'm either waiting around, with the lens sat on the tripod (shooting at a good shutter speed), or i'm hiking through bush/unstable slopes and I'd have to affix the monopod and then extend it before I could think about using it - in which case I may as well have just set up the tripod. For the latter situations I either hand hold or rest on a rock/tree branch etc and shoot at a decent shutter speed.*
Monopods are great if you're relatively stationary - such as at (motor)sports events where you move a little, but nothing major, and have lots of space to wander up and down.
*Obviously for the latter situation I wouldn't be doing it with a 600 f/4, but with a 300 with a decent shutter speed and IS then it's not a problem. If you can't get a decent speed then subject movement is going to be the biggest issue.
EDIT: I have actually had a monopod for years, I've tried using it multiple times and I just don't get on with it, I prefer to keep a high shutter speed and hand hold instead, there is just far more flexibility for movement.
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