Head Weblink the manufacturer of HDRM200 have released a different variant of HDRM200, with an MT7621 CPU instead of MT7620A. After corresponding with them they have confirmed this change. Could do with adding a comment on the hardwaredata page to reflect that (or maybe it needs a new page altogether). I would do this but I don't have an account for this.
They still call it HDRM200 which is annoying, the only visible difference is the PCB is labelled HDRM200-V1.3
It's likely the bootloader is also slightly different to reflect the different CPU.
In terms of OpenWRT support, the MT7621 EVB target kernel image boots successfully from TFTP, but it does not detect the mtd partitions, presumably because the generic dtsi file does not have the specific partition definitions. When writing the sysupgrade image to flash it does not boot at all, probably for the same reason.
thanks @tmomas - I'm not actually sure what I would call the devicepage if I made a new one as there isn't an official name for HDRM200 rev 2 - maybe I'll just add a comment to the existing page for now?