Would you recommend using a personal tether attached to the Sunny or Safari to prevent it from running away in windy conditions?
I think it’s as like I was told in the military, “it depends on the situation and the terrain.” Most paddling is nearby a shoreline in calm conditions, so a boat tether does seem unnecessary to me then. However, if I was going to paddle by myself, in an exposed crossing well away from shore, in wind, a boat tether makes sense as a backup. However, I don’t recommend ever paddling alone in those conditions. I also would never have a boat tether on me in a fast river.
A boat tether is also a potential entanglement for you in the water. If you are wearing a PFD and the proper clothing for immersion, you will have time to sort out your paddle, the boat, the various leashes and tethers, and get back aboard.
The best advice I can give you is to get your kayaks into reasonably warm water and try dumping yourself out and reboarding. Try it in the calm, in a little wind, with and without the leashes. Your Sunny will be easier to re-board than your Safari. The important thing is to try your safety gear in real conditions. You might find that the length you thought would work on a leash is actually a liability, or that you guessed right.