If two participants are in EU, the latency is awful. I don't get the impression they have multiple POPs.

I'm based in the EU (until Brexit anyway) and often do calls with mainland Europe. Never had that problem. Seen a high CPU warning a couple of times but it goes away. Overall I'm a fan. I have friends who use it for virtual conferences even.

Do you have people using the POTS gateways?

I use the free version out of the box to onboard new people (mostly independent coaches/consultants from around the world) as partners - see https://www.agendashift.com/partners to get a feel of geographic coverage