lol, at the late analysis in this thread. C'mon guys you aren't acknowledging the facts at the time. One of which is that #11 was playing with cracked ribs and/or a dinged shoulder. He's playing with alligator arms, dropping balls he'd never drop, not getting his arms up to try to bring down balls. His timing with Brady is way off - he's coming out of routes a tick late. All of which points to his injuries/dings being more significant than they've let on. At the moment they picked up Sanu, they probably figured that Edelman wasn't long for the year - and given everything that was going wrong on the receiving side - figured they had to ensure Brady had at least one slot receiver.
Additionally, no matter how good you are - you don't just recover from a high ankle sprain in the time Sanu seems to have. He is playing dinged as well. Asking a slot/possession receiver to play with a balky ankle is asking for no separation.
The relatively high number of trick plays this year indicates to me how concerned they are with the offense right now. The White throw? damn, years ago BB wouldn't let Edelman throw the ball, never mind the 3rd string trick play QB. They are trying to survive any way they can. In that environment, 50 different roster decisions could be 2nd guessed, I'm just not sure that Sanu is one of them in the context of the 'moment' of the trade. That's not including what the team knows that we don't, both on injuries, practice performance, and the tenor in the locker room (perhaps near the TB#12 locker).
Finally, the trick plays they save for the playoffs? It would shock me if Edelman and Sanu (and maybe Meyers) haven't been designed into some "double/triple half-calf mocha with a twist" plays to be unveiled in the playoffs. Pressure the league with a speed/power twin towers approach at TE when no one else is doing it? Check. Going with a power running game in the playoffs last year when the league is passing everything but kidney stones? Check. Going with 2 (or 3 if you count Meyers) slot receiver sets to screw with a secondary (or counter a blitzing package) and protect an OL which qualifies as a Swiss Cheese OL even by the strict French frommage standards? Those plays are waiting there beckoning the team forward like the 9 2-point conversion plays in the Falcons Super Bowl game.