I would not suggest stay away, but I would suggest testing it yourself.
I personally found the S-series to be slow and a bit flaky. I had no issues with sound quality.
The Phone Apps are horribly slow to use. I did not continue suing them long enough to figure out if it was the phone or the app itself that was slow. It did not matter really as whatever the cause, the end user experience was poor with it.
Regarding flaky, the BLF would not stay consistently displayed after a reload of the config. It would require a reboot for it to be brought back. It did not do it every time, but often. That is just silly. Again, I did not continue to use the device long enough to troubleshoot.
This kind of stuff should have had feedback before being released.
Maybe it is better now, I do not know. The S505 (or S500 I forget) that I have is still sitting powered off on the shelf in my office.
Compared to the Yealink T4X series that was current at the time, it simply was not worth the extra cost with those issues for the minor good features that it had over Yealink.
I get that Sangoma needs/wants a revenue stream to fund all the development for both the FOSS projects they lead as well as development of commercial solutions. I’m just not sure if their own line of phones was really the best choice. Or maybe there just was not enough R&D done to make it seem like it was a well designed device.
But it has now been 5 years since they acquired Schmoozecom and only a little more than a year since they acquired Digium. Personally, I am hoping they combine the Digium line and the Sangoma lines into a single GOOD phone line in the nearish future.