I fitted this at the weekend. I didn't buy the upgrade kit: I am using a standard E3D v6, except that I have a screw-in stud thermistor (http://www.ebay.com/itm/E3D-version-of-M3-Stud-Thermistor-for-Reprap-Prusa-3D-Printer-Hot-End-Hotend-/321490496841?var=&hash=item4ada53ad49:m:mLA3XrbhP8nnAylK0jesqhg). I had to trim back the silicone to fit round it.
I had some worries because only the very tip of the nozzle sticks out, less than it looks like on the E3D pages. I might need to back it off a fraction of a turn. Laziness has prevail so far: if I did this, I think it might need to tighten the heat break down again. I was worried that the sock might hit the print as a result, but so far this has not been the case. I've done a few small prints so far, and it keeps the temperature stable, and also helps filament sticking to the nozzle. This has been a bugbear for me, with ooze from before the print starts sometimes getting stuck and then deposited in the first layer. Filament does not stick to the silicone and I've had a cleaner start to my prints as a result.
Thanks for posting about that, animoose. I have the same thermistor and thought I too might be able to slightly trim the silicon sock to fit. Glad to know it will work. Looks like I'll be getting some new socks!