Received them today. I had to put 2 o-rings for some key caps purchased from SP, but other than that, it works fine.
I like the feel of it. It makes Cherry MX switches to have similar bottoming out feel of HHKB. (Instead of bottoming out on hard plastic, you are landing on some sort of rubber) The feel is most noticeable in Red switches, whereas in Browns and Blues the tactile feedback of the switches makes it hard to distinguish the effects of the o-ring.