I have a HitBox and quite like it overall. I haven't used it with Guilty Gear specifically though, so its appropriateness for it may be up for debate.
Overall, it's somewhere between an arcade stick and pad, and the placement of the 8 button takes some getting used to, as it is "lower than"/"below" the 2 button. Even after about 4 months, I still have some problem processing a midair 8d, haha. And processing particular motions that use 7/8/9, like Soul Calibur's Ivy's old Calamity Symphony input (376231), can also be pretty awkward at first. It also feels like I have to piano 4~8 or 6~8 a bit to get 7 and 9 jumps to come out.
The HitBox feels great for getting very clean and fast dashes, IADs, 236s (x2), 214s (x2), and 623s. TK'd specials are a bit different in that they are easier when ended on 8 (e.g. 2368). Charge motions also feel great, although [2]8 can feel somewhat awkward at first. It may be personal execution problems, but I have some trouble with half-circles (getting 4136 when going too fast) and 360s/720s, probably due to the fact that P4A and Tsubaki rarely use those, if ever.
The buttons feel relatively small (smaller than typical arcade stick size) and relatively sensitive to touch (can trigger when slightly brushed by the side of the hand), and the layout feels a bit tight. So it can be a bit uncomfortable and cramped for those with bigger hands. Luckily mine are small. =P
I'm not sure if it's the perfect controller, but it certainly has its advantages. Keyboard users would feel right at home on this.