Tell me why I should pay the extra money for the 500.  It is going to need to be more then just the pretty dispaly because I already have a better display then the 500 operating in the cab. 

I've heard (overheard really, I wasn't directly involved in the conversation) from a neighbor that there are things the + will do and the 500 won't.   I got the impression they were using the + in some of their operations because the 500 didn't work "yet"   I don't want to run into that sort of problem.  Is there a reason to stick with the proven product at this time?