I think the point of the Massoth DRC system, Matthew, is the versatility it gives you - if you have just one or two locos fitted with it, using a DPDT switch as suggested in the PDF that JonD linked to above to allow selecting either the battery power OR DCC track power, then you've pretty much got the best of both worlds - the ability to get full DCC control when running on battery (eg: when visiting someone else's analogue or live-steam line, or just when you can't be bothered to clean your track but still want to run something for a little while...) but to still use the same loco on DCC track power when available seems like a very attractive option.
As to whether the DRC units are actually available to buy yet, I'm not sure....as Colin said, Massoth's site still has them marked with "blue blobs" ("coming soon") rather the green "available" blobs, BUT it does say "Summer 2010", which is a while ago now - I can only assume that the production of them has been delayed for some reason; Massoth are still quite a small family firm, I believe, despite their high profile in the G scale world. Modell-Land's website, however, appears to list them as available to order, unless I'm reading it wrong, so maybe they are just on the verge of coming onto the market at last?
Jon.