Fairly popular in my neck of the woods and rock solid. I literally had a bad sparky put 230V through one of them. It killed the RJ45, it killed two client hosts on the same bridge, it killed the port, but the Switch itself continued to work. (Still replaced it, though)
The only thing I find them really bad and ironically replaced them with TP-Link (Omada )is Wifi. (and the fact that they let the promising "The Dude" die).
Security wise they seem to do their homework so far.
Their solution to central management (Capsman) is a burning mess, when WiFi6 came out for a long time(I think 2 years) you were unable to keep older and newer APs on the same controller, so you needed two Capsman instances. Roaming between them is very unreliable and generally their hardware is underwhelming in terms of antenna quality, etc.
For one AP it is not as bad, but still annoying, if you want to centrally manage more APs it is a nightmare.
I replaced my MK APs with Omada with the software controller on a LXC and couldn't be happier - they play along nicely with my MT infrastructure and are way more reliable.
I really love MT,but not their WiFi.