The chainline for an ENO hub is 47.5 mm, which, as you read on Sheldon's site, is close to the outer ring on a road double. I use an ENO hub with a standard Shimano Octalink double bottom bracket, Shimano 105 cranks, and the chainring in the outer position. The chainline is very close to perfect with both a White freewheel and a track cog. I use single stack chainring bolts rather than spacers.
The ENO hub is fixed/free - one side is threaded for a freewheel, and the other for a track cog and lockring.
The two cogs on the DOS ENO freewheel machined in place and not independent of one another.
The eccentric ENO hub generally doesn't have the same range of adjustment as a bike with track ends. When the eccentric is in the "12 o'clock" position, your rear tire may hit the brake bridge. In the more forward position (about 2-3 o'clock), the chain may be too tight.
Be prepared to experiment with different cogs and chainrings until you get it just right. I've found more range of adjustment with smaller cogs/freewheels and chainrings, for example, 44 x 15-16-17 vs. 54 x 21-22.
The hub is great - I have a couple!