Hey,
I used a dual action (I'm assuming this is the kind with the arms that swing) while recovering from cancer and a semi-paralyzed arm. In that state it was good because I couldn't really walk and the moving handlebars allowed me to get more of my body into the action.
That having been said, for someone who's fairly fit, I don't see the advantage. The problem I've found with mine as I've gotten back to normal is that the arms move with the pedals, so there isn't a lot of resistance unless you sort of scale back the power you're applying to the pedals, at which point you pull harder with the arms. This can work okay but I can never get a very good rhythm going in which I'm balancing both the leg and arm power, so my arms just end up going along for the ride.
I'd go with a good trainer or even a set of rollers.