Other than cost, I'm not sure there are any cons. The main pros are firmer shifts and reduced temps both of which are a noticeable improvement. The other pro for me is that the extreme valve body allows manual lock-up of the torque converter in all gears.
I used a A343 body from Wholesale Auto. It was WAY too firm (i.e. No slip between 1-2 into gear especially in 4lo), but it did reduce trans temps, based on my trans gauge. I ended up going back to stock.