This response always causes - sharp opinions.
This is my point of view - I started kiting in 2003
I bought a Naish - it had de-power (good by the standards of the day), you could flag it and it was well built.
I also bought a combined harness impact vest a helmet and a reel leash.
I figured once I had the kite back in the air after a crash (much slower in those days) I did not want to go looking for the board. I learnt how 2 body drag upwind and could recover a board when not on the leash.
When do I recommend using a reel leash... any where you....
1) can't touch .. are not in the surf and there is a current....and you are not doing jumps / deliberate aerial manouvres...
But I always wear a helmet(religiously) and rarely attach a leash.
I always have a leash to attach when the wind is light and I am in a tidal flow.
You will find you out grow the need for a reel leash - but every kite shop has them.
I would not use a surf board leash - it is likely to load up under pressure and can release towards you - you can get hit - a reel leash has a spool of tough webbing material about 2 metres long - crash loose the board and it spools out behind you, and in my experience has never come close to hitting me.
The points to understand - once the wind picks up a leash can cause the board to anchor by digging into the water and if you get lofted by the kite it can pop under tension out of the water - it may hit you.
The very well meaning opponents to wearing a leash are all likely to have great board skills happily jump turn in 10 cms of water 50 cms from the beach and rarely loose their board - you will get there - in the mean time if you do not want to loose a board when it will not come to shore by itself due to current etc try a reel leash + a helmet - you should learn thru' its benefits fairly quickly and stop using it - all part of the learning curve.
Cheers
AP