Nah, if it's meant to be used with a double, I would think it would need more separation. After all, the front rings will be a full width apart--I suppose you could have the outer cog float in the air, leave room in the center to fit a lockring inside it and around the lockring threads. It seems like a stretch, but what do I know? The separation between the two cogs does seem pretty substantial.

I guess it might be nice for people like me who have a flip-flop fixed/free but would like to have another fixed option or for people who use the free but would still like another gear.

It'll be interesting to hear from someone who actually uses the thing.