The small cintiq’s can also be used in a desktop scenario, but yeah - the idea is that you can easily transport it, say take it to the library or coffee shop. There are different versions, including one that is a proper tablet (no additional laptop/desktop required).
Well, I haven’t used a Ugee so I can’t say whether you’ll experience the pen range issue, but based on the reviews I’ve read it sounds as though in general people like it better than the Huion. You should do your own extensive research though.
The Ugee’s resolution is no worse than that of a 22 inch Cintiq (1080p), and though it has no display port it does have both hdmi and dvi, either of which are perfectly adequate. It’s a fallacy to suppose that your losing anything significant from the lack of a display port. The first Cintiq competitors only had a vga output, now THAT was ridiculous!
Provided that there are no weird issues like the pen-range thing, the only feature that you are very clearly losing by not selecting a Cintiq is the pen tilt sensitivity, and as I’ve explained before there’s a very good chance that you wont miss that, especially if you primarily expect to work in ZBrush where that feature has no effect at all… Well you are also missing out on the monitor side buttons, but I have never felt inclined to use those when I had use of a Cintiq and I know many other’s never use them either.
Just remember that yes - there’s a good chance you’ll encounter some finicky behavior from a non-wacom product, but you will likely be able to figure those out and work productively with the item anyway. You are taking a gamble - that’s the price you are paying to save a good chunk of cash in the short-run to tide you over until you can justify the more expensive purchase of a Cintiq. Ultimately, only you can decide whether you can better afford the gamble or the premium product. For myself I think the gamble worked out for me, but it may well be that putting off the purchase, using a regular tablet in the interim (go cheap on this), will be the better route for you. that depends on how quickly you can raise the money for the sure bet of a Cintiq. Anyway - I should stop now before I start going in circles:)
Out of curiosity - what are the specs on your $8000 system?