I’ve had mixed experiences dealing with Finn at Domains.coop. I’ve found him to be very courteous and helpful on the phone, less so in support tickets/ emails (but that could largely just be lack of body language and tone of voice).
But overall I find the customer experience of domains.coop to be pretty bad - they just don’t have good infrastructure in place (as per Is there a cooperative domain registrar? - #2 by chris it is all outsourced to https://www.realtimeregister.com/).
Once I learned from @chris than Gandi.net do .coop domains (about £30 cheaper than domains.coop) I started using and recommending them instead (they know what they are doing and run their own infrastructure).