I've used the M201 atty on my Vapre51 since day one.. love it. As far as the cartomizer on the Vapre51, when compared to the M201 atty on it, it depends on how 'fresh' the cartomizer is. When first used, or just after filling, the vapor production will definitely be lower, but the flavor will DEFINITELY be there. The first few hits after a refill, hit you like a freight train with flavor.
The more you use the cartomizer, the more vapor it produces, until it goes dry. At some point the cartomizer should be putting out an equal amount of vapor, compared to the M201, once broken in. I can't tell you exactly how long the cartomizer will last, as everyone's habits are different, but my cartomizers are lasting at LEAST twice as long as a M201 cart.