Thought I would just share my experience with the TOP (7 brews). Overall I have been very happy with the system and have had only a couple of issues to work out.
I double checked my thermometers and know the thermapen and the TOP sensor agree within a couple of tenths of a degree with each other and the brewmometer reads about 1 degree high. For MY system, it appears when I brew a big beer (the mash tun is very full) the temp on the TOP controller is within a degree of the mash temperature when checked with my thermapen. When the mash tun is 1/2 - 3/4 full, the difference has been as much as 5 degrees and I have had to adjust my temperature on the controller to achieve the correct mash temp. I think the reason for this is the outside air temp for my brews have been in the 50s/60s. It will be interesting to see what the difference is when brewing at higher outside temps.
I've actually brewed 8 batches but one of the mashes became hopelessly stuck (and one other close one) because I did not follow Blichmanns instructions. You have to wait 10 minutes AFTER doughing in before you start recirculating. I also took their advice and have now been using rice hulls with every batch. In the last 5 batches I have had no problems.
Here is a YouTube of my system: