I ponied up for the full subscription last year when they added MLB.tv support for the Apple TV, and it's great. Being able to watch not only on the the phone/iPad but also on my big TV put it over the top.
The only annoyance is MLB's draconian blackout policy. If I'm away from the house and want to watch the Braves, I have to use my Slingbox instead of the MLB app because all local TV broadcasts are blocked. It should be a no-brainer for anyone who roots for a team out of the market they live in, though.