You probably have read my preliminary review on the premium leisure. I will do an update soon. I can tell you this at this point: Since that review I used the tether that came with the unit and I like it very much. I don't find it obtrusive, cumbersome or uncomfortable. I have used it with and without the propeller and it works well. Using it with the propeller allows you to change the intensity of the workout. The advantage I see so far about using the tether is that makes your swim experience more forgiving. For example, we all have a tendency to be stronger on one side - the tether pretty much helps you to stay in the center and also prevents you from hitting the end of the swim spa if you overcome the current momentarily. Since trying the tether, I have been doing all of my exercising with it. I believe Premium Leisure and I am sure Endless does also, sell a treadmill and a rowing attachment as options. Hope this helps.
Boone, you have the swimmers edge 18 model, right? How much did you pay and how do you like it after having it for a few months? i'm considering buying one.