Have no fear of buying them used. If (and that's a big IF!) they wear out, Dillon will make it good. The 550 is an excellent first loader, does rifle, and is pretty upgradeable.
Yeah, I'm not worried at all. This guy takes care of his stuff and he says that the 550 is still in excellent condition.
If I start with the 550, I'm really not going to miss all the bells and whistles of the LnL or 650, cause I've never used them! I'm sure I'll upgrade one day, but this one will last me quite a while.