I would say honestly if you have the older ones and have them mounted as you like them, keep them...The new ones are slimmer yes but they have a big capacitor box on one of the lines going to the bulbs and it is annoying to have to tie them up too so I can't spool up the wires...They work just as well, I have both sets here and currently have the new ballasts mounted but I wouldn't hesitate to keep running the old ones.
For your wife's quad yes they are a good buy for sure, just takes a little more imagination where to put stuff at, as you see in my pics.