they are alright, same with allmakes and britpart. they don't make the parts but buy them in, so they are really part suppliers.
sometimes the parts are great, sometimes a bit ropey.. britpart tends to be on the ropier side as a greater percentage, however they probably ship a lot more product.
saying that, i still order britpart stuff for some items. you can usually tell if it's any good by looking at the build and finish quality.
btw, oem or part numbers ending in G are meant to be from the genuine supplier.
this again is a bit murky as it seems a lot of companies class oem/g as from an oem supplier.. but that doesn't mean it is still an oem supplier or that it was oem for that part.
it's all a bit sketchy isn't it
in general, buy branded (timkin, delphi, trw, etc) for things that are a bugger to replace or that need to be of good quality. ie oil seals, wheel bearings.
lrdirect usually lists the brands, island4x4 too for some things.