I have the net inner, and it's a pretty small space. If you lay still it works, if you sit up or move around much, you're running into mesh. You have to put pretty much all of your stuff outside of the net inner tent, so if you need to mess with your gear at all, you're opening up the mesh. It works, but it's not my favorite piece of kit.
The height/length and just generally overall space available inside the G.C. does vary based on how high and just generally 'how' you pitch it. With a second trekking pole and then maybe a local stick or overhead branch, it certainly does help to pull out the loops on the long ends.
I personally find my G.C. the right piece of gear to bring along (a) on extended day hikes in decent weahter where it seems prudent to bring along some sort of emergency shelter, (b) short (1 or 2 day) backpacking trips where the weather looks pretty good and it's not likely to be buggy.
For other trips I prefer a 'real' lightweight 3-season tent.
I have a friend, though, who used a Wild Oasis tent for long distance hiking and seemed happy enough with it. Wild Oasis is also made by SMC and is basically a G.C. that can't be used as a poncho, and has added a little skirt of bug mesh --- still a floorless tent, but the mesh skirt worked well enough for him (and of course left a lot more usable space inside than the G.C. with its dedicated inner net tent).