This is one of those questions if you ask 50 people, 25 are going to love it and 25 are going to say it is useless. On the older 545rfe I think it worked better because the trans didn't have the same learning logic as the newer ones do.
I will say I have an 09 with the newer 545rfe and have the sonnax on and I think it made a difference. Sure the first few days were nice, but then the learning logic of the trans kicked in and adjusted the pressure back down. Even after all of this, my 2-3 shift is hands down better than it used to be. Before the Sonnax, it would have a long pause (like it was thinking where to go next) before it would shift. Now I have none of that and it shifts just like it should.