I'm a TLS owner with the full TKS. POH states 2h30 at normal flow from a full 6.3 USG tank (6.1 usable) including 'intermittent' use of the screen de-ice sprayer.
For the performance, the general feeling on the longbody list is that the install will cost you around 5-7 knots. The POH has a statement somewhere about it reducing the climb performance, I'll see if I can locate it and pass the figure back. A full (FIKI) install adds 35 lbs, and then a further 57 lbs for full fluid
I've used it a couple of times in anger this year, once at FL120 over Geneva, and a week ago at FL100 going to Troyes. For the latter occasion, I could have easily climbed on top, but it was a relatively short hop, so was happy to switch it on and let it do its stuff. Do beware though, if you take off into the freezing soup without having primed the system, the build up can get significant before the fluid get to the extremities