the problems w/ the majority of xs pwr kits i've seen:
1. bov causes vac leaks because the top doesn't seal.
2. bov causes boost leaks because the piston doesn't seal.
3. poor manifold materials/welds cause it to break quickly.
4. same manifold used on most of the kits so it may not be a/c compatible like they say it will be.
5. wastegate and/or placement causes boost creep.
6. boost leak before turbo because collector not always welded fully.
7. charge pipes not bolt-on w/o being modified...may not be bolt-on like they say.
8. poorly constructed turbo's fail quickly...sometimes before the first week is over.
9. no/poor fuel management.

a lot of this adds up to fix/modify and you end up spending much more up to the cost of a custom kit installed at a shop.

i would recommend the mainstream kit installed over one of these anyday.