I wanted a smaller design and went with the lest costly Tomtom multisport, just based on size. This is from another post :
This Tomtom I got has a pool mode , which uses accelerometers,( of course, because GPS doesn’t work indoors). I have not tested this because I am swimming outdoors.
GPS also won’t read underwater. As soon as you put the watch under the surface the GPS is lost.
So for open water, I put on the TT on the wrist in RUN mode, GPS will still take readings but they are false (too much distance), because the arm is travelling in a loop and in and out of the water. Garmin has come up with a model-based program or equation that makes the arm mode usable. My Tomtom doesn’t have this and I agree you can’t be chasing a GPS signal on a swimmer’s wrist & still be accurate enough.
Also I believe it’s not a good idea to swim with a watch on one wrist.
So the workaround is to swim cap the GPS module and use RUN mode. The Tomtom detaches from the wrist band so no problem to do this. First swim today 7am straight up off the dock and got good data over: Distance 1500M
~$150 Tomtom Multi-sport https://www.tomtom.com/en_ca/sports/multi-sport/products/
I did not get the heart-rate monitor, I am waiting for the upgrade to the defibrillator. 