I've run a set of spidertrac adapter 5x4.5-5x5 that were 1.5" thick on my TJ and had absolutely no problems.. Like already stated buy a quality set, install em with the lock tight, torque em down, drive 500 miles then retorque. Most of the issues ive seen with em have been from being over torqued, no lock tight and never rechecked. Some folks will say that they put more stress on the knuckles or bearing being an eccentric load but they are the same loads as putting rims with different back spacing tha moves the tire 1.5" out.
I've got a CJ on 38.5 boggers that has a slight clearance issue with tires rubbing the front springs so I will be installing a set on that.