If I had to choose between purchasing the OpenWrt One or a Chinese equivalent from AliExpress, I would prefer the OpenWrt One. Although I'm not particularly fond of the manufacturer due to their tendency to frequently release devices and then either barely support or not update the software for them, in this case, it's a good combination of price, hardware, and OpenWrt, with which support is unlikely to be an issue on this device.

Unfortunately, I had already purchased a similar device from AliExpress and spent a lot of time experimenting with firmware. But... Filogic is very fast; it's probably the fastest OpenWrt router I've had.

The HG612 will be plenty fast enough if it works, it doesn't really do anything but pass the traffic to pfSense.

I think you will need it unlocked to change to bridge mode. That's quite easy though.

I hope it's the 3B version. Some of the earlier ones had known over heating issues.

Steve