Also curious about the 610. Is that the one that doesn't supply phantom power? Not that you'd need it for a RE-20.
If you don't mind running on batteries, the SD MM-1 offers up 66dB of stepped gain. And a few other bells and whistles. Limiter, low cut, quite a few power modes. It came with a power connector, but it's just the connector. As in what plugs into the unit, but not any of the other thing(s) that it would otherwise be connected to. Noticeably better than my Korg MR-1000 preamps, which were marginally better than a DMP3. IMO. Rated to 20 hours on 2x AAs without phantom power turned on. Supposed to be in proximity of 4 hours with phantom power. Depending on your greedy mics. And if you use the monitoring bell/whistle.
The RNP is actually made in/near Austin, TX. Which is in proximity to me. Although I don't think that it's as well received as the 610. Not that I've ever used one (yet).