I tried a number of things like you have suggested and not one of them was close enough to a real swim feel for me to stick with it. The Vasa is not perfect, but for the time-constrained athlete or someone who just can't get to a pool, it is a solution. Frankly, I don't understand people's hang-up on the price. Since I bought my ergometer I still have spent two or three times the price in other bike equipment. If you are riding a second-hand tri bike that cost $500, then maybe the Vasa is expensive, but it does not even hit the "entry-level" tri bike cost that is sold these days.
I suspect were a beginning triathlete to ebay a cheap bike and pay the full price for a Vasa, they would be a much better triathlete in one, two or five years.
Heck, since buying my Vasa, I have not done more than four or five pools swims in ten years. No cold water, no chlorine, no closed pools that you don't find out about until you walk in, no wet workout gear.
More specifically to your question, the bands tend to jerk your arm back and don't have a linear resistance. You can't do a overhand recovery with the Vasa, but the feel is very smooth and simulates the recovery better. It just feels very much like swimming. I never noticed my arms getting tired on the recovery in races when I was doing 100 percent Vasa swimming. The swim is a weakness for a lot of people and the Vasa can address some percentage of the problem, i.e. swim fitness or lack thereof because of minimal frequency. If your form is horrible then it can't help you there, though I think it may have improved some part of that for me because it is hard to use the Vasa without employing the early vertical forearm when you are training.
Edit: If forgot to add that if I was a little more mechanically inclined or was trying what you are trying, I would rig some sort of pulley system with weights, rather than use the stretchy bands. If you set up a 2x4 at bench level and used a couple of smooth pulleys with a bearing in them, you could probably duplicate the swim motion, it would be a more linear resistance, and it would not wear out like a stretch band elasticity. The Vasa is essentially ropes with paddles using a pulley attached to a large flywheel.
I suspect were a beginning triathlete to ebay a cheap bike and pay the full price for a Vasa, they would be a much better triathlete in one, two or five years.
Heck, since buying my Vasa, I have not done more than four or five pools swims in ten years. No cold water, no chlorine, no closed pools that you don't find out about until you walk in, no wet workout gear.
More specifically to your question, the bands tend to jerk your arm back and don't have a linear resistance. You can't do a overhand recovery with the Vasa, but the feel is very smooth and simulates the recovery better. It just feels very much like swimming. I never noticed my arms getting tired on the recovery in races when I was doing 100 percent Vasa swimming. The swim is a weakness for a lot of people and the Vasa can address some percentage of the problem, i.e. swim fitness or lack thereof because of minimal frequency. If your form is horrible then it can't help you there, though I think it may have improved some part of that for me because it is hard to use the Vasa without employing the early vertical forearm when you are training.
Edit: If forgot to add that if I was a little more mechanically inclined or was trying what you are trying, I would rig some sort of pulley system with weights, rather than use the stretchy bands. If you set up a 2x4 at bench level and used a couple of smooth pulleys with a bearing in them, you could probably duplicate the swim motion, it would be a more linear resistance, and it would not wear out like a stretch band elasticity. The Vasa is essentially ropes with paddles using a pulley attached to a large flywheel.