I have one that I have been using off and on. I also have a CycleOps JetFluid Pro Trainer.

1) It works great for high Cadence work.
2) Adjustments may vary per bike (I cannot use the wheel weights due to the way the frame built-in cadence/speed sensor is, but still works fine without the weights, just first few pedal stokes feel odd, once spinning feels normal to me)
3) Gearing for the same cadence at the same power level is different between the 2 trainers, and I think the JetFluid matches the outside gearing better.
4) I find that taking the bike off and on the trainer is much quicker with the JetFluid, because of having to set the magnets back into position properly.
5) Looks like you could use the Stac Zero with any bike, with the adjustability of the resistance unit, and the way the skewer holders are made (My Aero Skewers obviously still do not work)
6) No pressure on the back tire, so you do not need to worry about airing it up, using and old tire, or using a trainer tire
7) You can keep you outdoor tire on and get no extra wear.
8) Have to use Aluminum Rear wheel (May work with just Aluminum brake tracks, but cannot test that) for the resistance unit to work properly.
9) Stac Zero is very quiet. All you pretty much hear is your drive train, which is pretty awesome.


Updated to add #9

Thanks for sharing!

bottom line- which would you recommend? STAC Zero has interested me but I have read very little about people actually using them. Would like to know if people would recommend them over a regular trainer.

Thanks for the insights. Which version do you have? Base or Power? Kickstarter or a later one?

Do you use it with TrainerRoad or Zwift? I've been toying with the idea of buying one, but I currently use virtual power on TR and it doesn't look like the StacZero is support yet.

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Strava

You can pay 100 Canadian Dollars more, or an additional 4 ducks, a goose, and 2 loons, for the power meter version of the Stac Zero.

I had a Kurt Kinetic road machine. When I moved into a new apartment that wasn't on the ground floor, I was almost murdered by my new downstairs neighbor following my first session.

I weighed the options and ultimately jumped on a Stac Zero. Overall, I've been very impressed with it:

PROS:
- Very quiet - I have no concerns about jumping on it at 6:30am
- With the wheel weights, resistance is pretty smooth; almost as good as my Kinetic
- Stability - The platform is stable and holds my bike well
- Andrew - The founder is extremely helpful and responsive to questions/concerns
- Storage - It folds down incredibly compactly because there's no resistance module

CONS:
- Quick release - There's no quick release like my Kinetic so slightly more work to take bike on and off
- Magnet Placement - It takes a bit of experimentation/tweaking to get the magnet placement dialed
- Super High Effort - If you're planning to do work well over 400W, it can be tough to get super high resistance

Ultimately, I needed something super quiet, and the price of the Stac Zero was definitely worth a shot compared to TacX Neo (at $1500). I'm really happy with my decision.

Hard for me to fully decide which I like better.

I have the Power version and got it through the Kickstarter Campaign. Have not checked to see if they have made any improvements, or major changes since.

I can tell you that the power output in the few rides that I compared it against my P1 pedals was within about 5-10W, which since one is pedal based and 1 is based off the rear wheel, that is not bad.

All 3 of my Garmin Devices 2 watches and 1 bike computer picked up the power fine, so if Zwift or any of the other ones connect to any powermeter (ANT+/Bluetooth Smart) then I would not see why it wouldn't work, but I do not use those programs, so I cannot say for sure.

I'm surprised at this. I would expect it to have a screw-type adjustment for first-time use, then "open" and "closed" lock positions. Is that not the case?

It seems like adjusting the magnet proximity every time would lead to inconsistent resistance.

Agree completely. Think I laid most of that out, but you spell it out better. Also have to agree that The founder Andrew was very helpful and very fast to respond.

Nope there is no open and close lock position. Once you have done it a few times it gets pretty easy though.

That is the one update to the product that I think could be beneficial.

They just use a quick release style clamp to hold the 2 magnet arms, and it seems like people have had some issues with consistent resistance, since they have a couple of youtube videos that show how to adjust the spacing, plus they have a plastic tool to help you set the gap to 3 different distances now.

Yep. I have used the tool. it helps. I usually just set it to the smallest setting. I think the Wheel weights help to add a little resistance too, but like I said, they do not work on my bike (Too narrow between spokes and built-in cadence/speed sensor holder).