I use OPNSense, but I have used pfSense on these same configs, these are more top of rack and aren’t exactly 2U, but they’re cheap, incredibly power efficient (less than 15w at idle), powerful and tremendously reliable:
Dell Optiplex 3040 SFF, I use the i5-6500 models. These have a front fan, a PCI-E 16x slot and a 1x slot, an internal m.2 slot and dual SATA ports. I have 16g (LP DDR3) RAM in each, some mirrored 128g SSDs in each one (ZFS) and Solarflare 10g dual port NICs in the 16x for LAN plus dual port i226 2.5gig in the 1x for WAN. With 2 you can have zero downtime and don’t have to rely on virtualization which I try to avoid with routers.
Best of all, they get their own UPS and can run for hours on UPS power because they draw like 10-15 watts.
Sounds kinda weird, but I LOVE them and they are the edge of my network, which is substantial; 1.25g WAN, 100+ IPs, 4 APs, 10TB+ monthly transfer.
I use ECC Ram in just about everything, but because of the efficiency of these (again, consider UPS power draw in the event of an outage, that’s the key selling point here, plus low monthly power costs and low draw on generator when needed) and the size, front fan, and Dell server quality power supply, complete reliability, speed, low cost, one thumb screw to open, etc, I couldn’t be happier.