I can't yet speak from experience (we're building our pool now) but because our pool is not huge and won't have a very long swim lane, I decided to get a swim tether. I contacted both owners of the two big swim tether companies: SuperSwim and SwimTether. I spoke to both and asked them the difference between their products. The SuperSwim guy sent me a very long and very detailed email response. The SwimTether guy ultimately talked to me over the phone. In the end, I believe both products would work almost equally as well.
The biggest difference is that the SuperSwim is one single pole made of fiber glass compost - the rope used between the pole and belt is just rope - all the elasticity is from the pole itself. Also the SuperSwim belt is riveted together w/stainless steel (not fabric stitching) and their comfort pads are made from a soft rubber and infused with high quality UV protection from the sun. Also the belt isn't really a belt, it's a sling with a stainless steel clasp.
The SwimTether on the other hand is a two piece pole. It doesn't have as much give as the SuperSwim so a rubberized cord is used to connect the belt to the pole. (In theory, the rubberized cord would be something that would need to be replaced more often.) Their belt uses wet suite material (whether this is a pro or a con I assume depends on who you ask) and is held together using fabric stitching and a plastic fastener.
I wish I had been able to try each one and decide based on that, but since that's not possible I used the above info to decide. Ultimately I decided on SuperSwim. But the reviews I found were good for both.
Also, before you buy, look online for discount codes. I believe there is one on a YouTube video for SwimTether and I found one on SuperSwim's twitter feed for 10-15% off before I ordered mine.
Still waiting for the pool to be finished to try it out... About 2 months away.
