A tow tether on the PFD is handy if you needed to quickly clip on to an empty kayak or paddle and tow back to the owner. Not so comfortable for longer towing so a quick release tow system on the kayak itself should also be considered. Practice using before you actually ever need these tow systems. I have been advised to always have a knife in an accessible place whenever using towing systems and ropes, just in case.
I have had a look at the Sea To Summit and it seemed flimsy, floppy to wear (in the shop) perhaps people who have used it on the water will have better advise on performance, also how the nylon handles the sun.
I got a second hand Stohlquist Tow Motion from a Kayak Guide who used it almost every day for a year and its still in great shape. I can wear it all day and forget I have it on its so comfortable.