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 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 v3, one 1.75mm TFT 255C teflon isolator but no bowden and no nozzles. The standard bowden works okay. Standard UM2 "olsson" nozzles work okay but you need 1.75mm nozzles if you want to be able to do a cold pull (not critical) (sold separately). I will give you a free ABS spring replacement if you ask for it in a separate email but it is not recommended because you need quite a bit of force (the spring is perfect) to stop leaks above the block.
I sell 1.75mm filament nozzles which can be used with this kit but ARE NOT NECESSARY! 3mm nozzles work fine with this kit.
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.