I'm using it daily, and while it does crash occasionally (but recovers fine after restart), all the features in TotalSpaces 2 seem to be there (including instant transitions and the overview). As a plus, it doesn't require SIP to be disabled anymore.
I have a feeling the problem of making it work was a bigger one than they expected, version 3 has been in the pipeline for a LONG time.
Seems there would be demand for such software based on the comments. For me at least TotalSpaces 2 has really changed how I use macOS, hopefully they will get it working on M1 & Monterey.