I received mine from slicksurf.com yesterday, a couple of people talked about it here and seemed satisfied
they're pretty cheap, shipping was 1$ for me (one set of four feet for a wmo), they're supposed to be durable but I wouldn't know

I really like them, I'm using them on a zowie g-tf and I'd say there's not much friction (which I find good but it's obviously subjective)

it's pretty easy to replace, you take a knife/cutter and slide it between the feet and the mouse to remove them, clean the glue with some alcohol and place your new feet, bam done in 5 mins tops

"amazink"