You shouldnt be telling him they suck, because a single coil size humbucker is just as good as a regular sized one,i got lots of both and just plain single coils and theyre all good.
But if someone wants a humbucker in a guitar thats not routed for it the single sized Hb is the way to go imo because it saves alot of messin around for no good reason.
imho the differences between a single and regular HB is ZERO!!!
the DiMarzio i got in my mustang looks just like a stock single coil,you cant even tell its there as i jammed it in the orig cover.
But if you want to stick with single coils then id say get some SD antiquities as ive got a 66 mustang and the pickups are realy nice and the antiquity is as close as youl get to a vintage sound.
just my 2 cents on pickups for mustangs.
Also a SD qp for jaguar sounds realy cool in a stang too,i had that in there for a while.