Seat Covers, Which Brands Fit Best?

First off, when installing custom fit covers over fabric, do you have to detach that large seatback flap that secures to springs under seat cushion??? The black strap in 2nd pic doesn't appear detachable.




We had some low 30s days here and wow, my cheapo leather cover didn't feel good in that cold. Also, leather makes me sweat even in high 70s days and I don't like blasting A/C. Is perforated better?

Is Clazzio leather or PVC without seat heaters a decent idea in 40 to 80 F SF Bay Area weather?

How well do GT Exact Fit covers fit 2010+ Prius? Any photos of GT seat covers on a Prius??

Do Wet Okole's feel at least as good as the OEM cloth, which is pretty good.

Coverking? Not sure I trust them as a good fit for Prius. Just cheap and everywhere on eBay.

Thanks

At 1:20 in this video, it shows Clazzio bottom cover pushed through the gap between seat bottom and seatback. Prius has a big flap that blocks the gap. Cover will not install as shown in this video. How do they get around the big flap Toyota put in to make it hard to cover the seat??