I have not used those, (or bolt in's at all) but I will tell you that I wouldn't even bother with bolt in at the sub frame points unless the subframe was fitted with tubes inside them to keep the metal from crushing.
Otherwise they will be pretty much pointless.
As far as having to weld those once fitted to the car, it wouldn't bother me a whole lot to blow the coating off and do it.
Be nice if you could get them to recoat after welding, but I don't see that happening unless it was paid extra for.