Hello, I have a TSA-120 with Feathertouch focuser. I bought it new December 2021, mainly because I wanted an FS106, but didn't want to wait three years to get it. The TSA-120 only had a four month lead time then. It is a fantastic instrument. I would highly reccommend it.
I have not used it with a full frame sensor, as yet. But I have used APS-C sensor (ASI 2600MM). Round stars to edge, with minimal vignetting at full focal length with Tak 35FL flattener and with the TOA-35RD 0.73x reducer. I have not tried it for imaging without flattener or reducer, but visually it is fine.
The Tak accessories are pricey, especially the reducer. The TOA-35 reducer with rotator, gives you a fully threaded solution. The flattener is a slip fit tube (like an eyepiece) with clamps. It ends up with two slip fit elements in image train to get proper back focus. This can induce some tilt, if all elements not fully seated. I have not tried a 3rd party flattener, as yet.
You can find examples of my imaging results in my gallery. One example of ASI2600 and reducer:
NGC 6604 ( Larry S ) - AstroBinClear skies!