While on the subject of ERG's, I heard over the weekend that FCRCC will be picking up two more machines that will be sitting side-by-side in their new gym that's currently under construction at the moment. Apparently this is so people can race each other all in the comfort of an indoor facility.
the marathon canoes are way better than the erg machine
I wouldn't say way better but I would think that they both serve a purpose depending on what level you're at in your paddling development.
Personally I think the ERG is beneficial for people new to the sport where they can be run through the machine while their stroke and technique is watched by their coach. It provided one-on-one time since you don't need to worry about the distractions of the rest of the paddlers on the dragonboat. I find it difficult to teach a newb on a marathon canoe since all you can really see is their back and I'm more hands-on when explaining technique. Of course this could be done on docked dragonboat as well, except that you would not be able to see how the paddler looks from a side profile from outside the boat.
With marathon canoes, I think it's more beneficial to intermediate paddlers since you're already got your stroke and technique down pat relatively (I hope...) and what you would need to work on would be what I'd like to call your "water-sense". These would be things like your connection to the water, your feel for the relationship between the stroke rate and hull speed.