They offer two types, the 'standard' ones are like melling or comp cams parts. They have a wire retainer. The 'microtrol' version has a snap ring style retainer and are what I'm running right now.
I went through 4 sets of comp lifters and all 4 sets were spongy after break-in. The microtrol have been rock solid so far. Never get any tapping, and comparing the workmanship on them to the last set of comps I pulled, it was night and day. Hard to explain the differences as they're pretty subtle and all has to do with the manufacturing, but it was obvious they were manufactured by someone who cared. No idea if I got some old stock though.