Hi Thorn,
It's obvious that anyone in favour of Leashes of any kind hasn't been in the sport long enough to know of the long, long list of personal injuries sustained by kiters using leashes over the years.
A customer of mine whom bought a leash to use on his surfboard against my advice almost lost an ear for his trouble. An ear hanging by a bit of skin and grissle isn't a good look.
Surfers aren't connected to a power source that doesn't stop instantly in the event of a crash.
What's more a board that flips up and through your lines is a total disaster as it pulls hard on one side of the bar due to the drag of the board which loops the kite and it wont stop until the kite crashes ...... if it crashes.

So you pull your safety to release the kite, but this doesn't help as now your being towed backwards behind a looping kite with the board stuck in the bar leaders with you totally seperated from the bar unable to reach it.
Yes you can say thats such a rare occurance, but it has happened to me once, and I've seen it twice and heard of it on another occassion.
If your life is worth less than the cost of a board, then you should march in and buy one straight away and let Darwins theory of evolution begin immediately.
If your upwind body dragging is so poor that it takes more than 1 minute to get back to your board (even in the worst crash) , then you need more practice, not a reel leash.
If you have a weak point in the line to your board so it snaps under excessive load, then doesn't that negate the reason of having a leash in the first place??? and then you can't get back to your board anyways???

I hate seeing people substitute gizmo's to make up for inadequate skills. UWBD is a fundamental skill as mentioned by bennie, and MUST be learned BEFORE you go riding a board.
Good winds,