I have exactly the same experience as phasor.
I bought my SSU in july 2017 and I use it intensively (3800 moves).
The issues that occurs too often and impact negatively the experience (and the reliability and the trust I put in it) are :
-HR problems, after 3 old Suunto strap it is better with the new version of chest strap (bought in march 2021) but it is not reliable enough.
-Sometimes there is NO GPS fix during several hours with no trace after the move, or it intermittently displays the no GPS signal screen and the trace is unusable. This despite the GPS assist up to date with Suunto app sync. This problem occurs often since las spring.
-Sometimes, when the watch memory is full of move it is unable to free some memory and the current move cannot be saved. Even after a night the wheel is still running and I have to push the upper right button 12s and the move is often lost with the reset. When the SSU memory is full of move, the saving time is very long and soon or later some move will be lost. The only solution I found is to reset the watch with Suuntolink and reinstall the latest firmware. This is flushing the internal memory. Then saving times are shorter again and no move is lost, until the watch will be full of move again.
Without these issues, the SSU has all I need. It could be better of course but the main problem is that I cannot trust it.
If the S9P is free of these problems and if Suunto is OK to make an interesting offer than I will continue with the brand because I like planning routes with the app and I am used to the Suunto ecosystem.
The perfect watch for me would be a S9P sized one with a bigger screen, no HR/SPO2 sensor (more room for screen and battery), and with a feature like the Garmin climb pro.