Please note that the ReNu product is available from many sources and at various price points. That was the first one to come up in a real quick search.
Richard (67gtasanjose) first researched that product. He has a few posts about it.
I got a small test kit which turned out to be a waste of $50 which, while it worked, was only good for a few vent windows. I need to do most of my windows! That will be a multi-day project and will involve the larger kit and possibly a few extra pads. I'm not looking forward to it since it's a lot of grunt work. Heck, I need to do the 2+2 as well so this will be a marathon.
Oh, I should note that to do this right you need to at least pull off the top stainless trim. An oak block and a dead blow takes care of them with NPD selling the tape.
The upper stainless and lower track frame is removable if you soak the window tape in a goo remover, so I wouldn't use frame or trim condition when looking for replacement windows.