XGP is made by Gamepark and the GP2X is by Gamepark Holdings, They are different companies. The XGP is looking like a closed source device with only commerical support, will probably flop like the Gizmondo.
I have a GP2X and it's good but dont expect to much, it's very much a work in progress (software wise) most software is made by single devs but give it a few months and it'll look even more impressive. Sooner or later there will be 3rd party frontends which will have better video/mp3 etc support
The device has potentual:
2x 200MHz CPU's - All apps currently only use one CPU but the 2nd CPU is hard to use as it isnt a proper SMP setup, it'll help once the devs work out what it's best used for.
64MB ram - 32MB is currently used for Linux but 3rd party apps will soon remove that totally and free up the full 64MB for apps.
Only downside is no 3d acceleration but it does have a hardware 2d accelerator, once again dont expect PSP quailty visuals but I'd say anything the original Playstation could pump out this could do better so it has the potentual for good graphics.
Battery life can be a issue if you are using crap ones, Get a good set of 2500mah and it'll last 4-5hours, buy 4 and you can just swap them over and recharge the others, in a way better than the PSP battery.