Slightly less accuracy than a full length (shorter sight radius).
Greater muzzle flash *in theory* but not in my practice.
Lighter. Better balance by far.
I have a shortie and like it. It has been 100% reliable so far.
It hasn't shown the theoretical drawbacks in my use.
Do shop with care, it is easy to buy a poorly made "tanker" but I like mine enough to get a shortie M1A if I ever decide to add that to my list.