I have used a range of different Watchguard firewalls over about 16 years.
The nearest model I currently manage is the XTM-21 which would be the next step up from the T10.
It uses the same management software. It has some extremely sophisticated options but you don't have to use these. If you get it out of the box, set up its IP addresses and do nothing else, it will still provide a serious degree of protection.
Management is from a web interface or a Windows program. Neither is particularly complicated for getting the basic setup running. I would be amazed if it was more complicated that setting up and configuring an open source firewall (and I'm a great fan of open source software). The Watchguard also has the advantage of smaller physical size and lower power consumption than a PC.
Watchguard support is very good so as long as you have a valid LiveSecurity subscription you can get answers quickly. Hardware replacement is also included with a LiveSecurity subscription.
If you have any specific questions, I'm more than happy to help.