STP is "slow" STP, and RSTP is a degenerate case of MSTP!
MSTP is Multiple spanning trees ie you can group VLANs and prefer paths for those groups of VLANs. That means if you have say two links between two bridges (switches) you can prefer some to use one link and the rest to use the other, that means you are not "wasting" a standby link. They will fail over to the surviving link on failure. STP and RSTP will only consider one link as a whole, so two ports are "wasted" when not in use: in the case of a two bridge, two links example.
Old school STP without the Rapid part hasn't really been a thing for several decades. I can't think of why you wouldn't use RSTP in general but if you need to make best use of your forwarding capacity then a 50/50 MSTP may be indicated. That's where you look at your traffic flows across VLANs and try to bundle them up into a 50/50% collection. One lot prefers link A and the rest get link B. Obviously you can get really creative as the number of VLANs and links mount up. Bear in mind that dot1Q is a simple version of QinQ!
Sorry, got a bit carried away there.
For nearly all intents and purposes, RSTP is STP. If you plug in a network cable between two devices and it does not start working within say five seconds then you are living in the 1990s.
I meant, where did you find that this specific Linux-managed network switch supports MSTP? Because the Linux bridge networking code, last time I looked, only supported STP; you had to run a separate daemon to even get RSTP.
