I like them. I own most of them now. Big Gear and Climbing were the ones I started with and branched out from there. I had a few of Chris Carmichael's tapes, but they got old....Lance this Lance that....20 minute straight set. Spinervals break things up change gears in long sets, Stand up, aero position, change positions. If you go to spinervals.com and look at some of the tapes, you can download samples to give you an idea of the content.

I have the remote tension adjuster for my trainer so I can simulate changing gears.

I use them quite a bit since many times I don't get time to ride until way after dark.