I've been using them for my domain and email for almost a year now and I have no complaints. I had to talk to customer support twice to fix a couple things that came up and they got back to me right away. Can't say the same for the last service I used lol

I think it's fair to point out they're not designed around encryption like proton is. It's not a factor in my threat model because I treat email as non-private communication, but it's something you should know if you're wanting proton for that reason.

kDrive is a heavily customized Nextcloud/OnlyOffice implementation with a pretty new and well-regarded file sync algorithm they implemented last year. I would recommend cryptomator to client side encrypt anything you want to protect. It's at rest encrypted, but not end-to-end because there's nothing client side.Here's a list of WebDAV urls from the Cryptomator community to help you set it up. KDrive is on there.

Anyway, hope it works out for you!