I must be one of the unlucky ones. I have TT1 and 2 TT5's and find them unreliable and inaccurate. I get 30-40% failure to sync at high speed and 15% failure to sync at 1/250. I am using Nikon D700 and SB800's. This after years of using PWII with 0% failure rate. My feeling is the TT1/TT5 are not yet ready for prime time.