I did my B&W 606 S2 with the upgrade kit, as well as adding No-Rez instead of the polyfill. The end result was definitely a significant upgrade. I am very happy with the kit. The little B&Ws are bi-wireable. So, I kept one of the posts and swapped one for the tube connectors.
When you are holding the binding post and spade and holding the tube connector, it just seems so clear it's a better connector. So many less 'connections' in the connection. The binding posts look fancier.
In my case, the tube connectors made a noticeable difference, but my gut is telling me it was getting rid of the low end spades I had on my cables. I have the ability to go back and test again later, but the end result, the kit fixed much of what I criticized about the B&Ws and took them to another level. For ref, this is a desktop setup, I have 803Ds on tube kit in my main system.
I recommend the GR-R kits and the tube connectors. Definitely worth giving them a chance in my opinion.