I bought the Harmony One to use with my main room setup (replacing a 670). I had an issue with mine in that unless the remote was precisely aimed at the TV IR sensor it would not control the TV. This was specifc to my TV only (Toshiba CRT). The One controlled all other components just fine (without having to be too concerned about where the remote was pointing)
I eventually had to use the One in a different room with a Panasonic TV and it has no issues there.
It seems it can be picky with some TV brands.