Zwift will change the resistance on most smart trainers and I believe, even works with the Bkool trainer. I use the Tacx Bushido and like it a lot, been using it close to a year now. I know a lot of people have been using the Tacx Vortex with good luck - I believe at one point, the Vortex was one of the cheapest smart trainers that would work with Zwift, but I think there might even be some cheaper options out now.

So with my Bushido, it'll match the resistance up to a 15% grade (if memory serves me correctly). It's also powered off of my riding, so there's nothing to plug in or turn on. I do believe the built-in power meter measures a bit on the low side, but it's still fairly accurate when compared to my Powertap P1 pedals.

As of August, this looks to be like the complete list of compatible trainers...
https://support.zwift.com/hc/en-us/a...Zwift-support-

The Bushido also worked with Bkool - I think most smart trainers will work with Bkool as well, but I'm not 100% sure on that.