It will be an exploration mission.

First, I can’t remember whether XTM 505 is x86 or not; Watchguard has a habit of mixing designations. There are similarly named models with x86 and non-x86 (usually, Freescale) processors. Other people say it is, so I’ll tentatively agree.

You most likely will not be able to run a Watchguard device with stock firmware. So you will need an alternative. The easiest one will be OPNsense nano; just replace the stock CF card with one containing OPNsense nano, and it will run. Same with OpenWrt; write it onto a CF card, and it will run. Or you can experiment with adding SSDs. This may of may not go well, because you may or may not be able to get into BIOS.

Performance-wise, XTM 505 will give you basic Gigabit routing no problem (except that one of the ports is actually 100 Mbps). How much noise it will make doing that will depend entirely on the state of the fans.

Peak power consumption on XTM 505, if memory serves, is 85W.

What you want to do with all of the above is entirely up to you…

One company I used to work for, we had an MSP on contract to basically back me up and provide 24x7 support. They were a Watchguard dealer and had many properties with WG firewalls onsite

We had Palo Alto firewalls at my company. During my tenure I got to know a lot of the MSP tier 2 and 3 techs, and we’d talk shop occasionally.

It seemed like every day they were rebooting a Watchguard on one of their client properties because it had locked up and become unmanageable, so they were basically taking businesses offline in the middle of the day to get the firewall back

I don’t know if it’s the hardware, firmware, or software that is at the core of those issues, but I am unabashedly NOT a fan of WG gear armed with that knowledge and experience