I've also been considering them and after the free trials it seems to be fine. I've heard of them many times in the past, and they've been around forever, so most likely quite reliable. Didn't have any problems during the trial. The web UI feels a bit outdated but not terrible. I prefer to use my own mail client anyway (Thunderbird)
One downside, as far as I can tell you need a business account (same price) if you want to use a custom domain and I didn't see any way to link multiple domains to the same account, but might just need a bit more digging.
Proton does look a bit more modern/nicer but it's also a lot more expensive.