The biggest problem with the vinyl tires on big rigs is they are hollow and can look flat since the sidewalls don't bulge out enough. I don't find this on pickups and cars as the tires are usually more solid.
There have been complaints that they will react to the plastic wheels as well (disolve the plastic), although I have not personally seen that happen. I have been told that was actually only a problem for a certain period of kits and the formula was changed but again I can't say one way or the other with any certainty. The tires also tend to be shiny, not bad for a truck with freshly armor-alled tires but it doesn't look right for regular tires. Easy enough to fix with simple weathering techniques, I find a wash of flat paint works fairly well.