I can attest to the HG612’s reliability. My Openreach-supplied one has behaved itself perfectly, running 24/7 over the past 8-ish years, with BT and Vodafone.
I too have a pfSense router/firewall behind the HG612. The modem’s in its default bridge mode. The only config change I’ve made was whatever tweak was required to get access to the modem stats over the same interface as the bridge.
I suppose I might gain a megabit or two if I switched to a different modem, but I’m already running stable at the maximum speeds for my line length (~55 in summer, ~60 in winter - temperature makes a huge difference to a 600 metre-long line!).