Both sound great, I have the RM500 and the OriginAL pedal. I’d say that you can do more with the RM due to the combination of drive/compression/pre-shape, these make it very versatile but for a solid good bass sound the OriginAL hits it. I use the pedal as my home-practice sound and it’s a really nice sound, tho the valve-drive set to anything other than fully off is far too much for me.
And after saying all that I’d be looking at FinnDaves RM800, and then keeping my eyes open for a lightweight cab that can handle 400watts at 8Ohms.