Why aren't these fixes in the USKP itself ? Is it advisable to use this ?

I assume you mean http://skyrim.nexusmods.com/mods/23833//?, and honestly I don't know why it exists. Most of the fixes are either already included or soon will be. It probably won't cause any harm to install it, but I'd just ignore it.

I would check in the USKP thread, ask Arthmoor and co. if that mod is affiliated with them. I haven't been in these parts in a while so maybe it is a mod I got out of the loop from. Doesn't hurt to check