DetailsI have tried this kit and it works great for me with standard bowden that comes with UM2 and standard 3mm nozzles. Some people have had troubles - I think it's critical to get the bowden into the green part included and even into the white teflon part and then the 1.75mm manages to enter every time no problem. 6mm retraction seems to be plenty - much more and you do run risk of the filament coming out of the teflon part and not going back in.
You really need the iRoberti feeder upgrade for this to work.
The existing UM2 style feeder is about 1.6mm gap when no filament is passing through so it doesn't grip the 1.75mm filament well and you may have to push the motor one way and the feeder the other and retighten the 4 screws to get it to be not "completely loose" in there. Much better to print the iRoberti feeder upgrade so you should do that first (search iroberti feeder on youmagine.com). I haven't tried this kit with the "plus" kit yet.
This kit includes a 1.75mm block, one 1.75mm TFT 255C teflon isolator but no bowden and no nozzles. The standard bowden works okay. Standard UM2 "olsson" nozzles work okay. Kit comes with a free ABS "spring replacement". I recommend using the spring replacement regardless as it guides the bowden into the teflon part nicely and avoids problems where filament gets stuck at the teflon part.
I sell 1.75mm filament nozzles which can be used with this kit but ARE NOT NECESSARY! I use 3mm nozzles with this kit and it works great!
No software changes necessary - simply tell the printer that your new material is 1.75mm instead of 2.85mm (under MATERIAL menu).
If you don't have the Olsson block (I believe all UM2 and UM2+ bought since January 2016 have this) then you need to get at least one nozzle also.