I started many years ago, flying only foils.
Windtools Mosquitos and Flexifoil Blades and the ultra fast Kitesurfer X-Foils.
Then I changed to LEI's.
But I have flown the 15.5 Psycho for a period, half a year ago.
So my experiences are mostly from the older foils (Except for the Psycho, which had great hang time), and not with the "latest" ones...
But still, at that time when I changed, I could compare.
I was a convinced foil flyer - as it seemed like the best "wing" at that time.
But there were downsides too.
The worst problem was gusty wind causing collapse (and worst case: tangling), and impossible relaunching when soaked up in small waves.
These problems got solved 100% right away, when I tried a Naish AR5 for the first time.
Stability and control in gusts, and "forever" relaunchable.
Of course they could luff and fall down in super gusty conditions - but it did not matter, as they could ALWAYS be relaunched.
I had to use a little time to learn to relaunch, as I could not back the kite up like used to.
But as this is part of the very basic training in any kite school - it did not take long to get used to.
The knowing that you never had to worry about tangling and/or not being able to relaunch, is really really an important thing, that make you feel much safer and better about everything - and you can really go for it (try every possible move), without ever thinking about the kite.
And then I experienced something I did not expect at first:
Much better hang time and easy control in the air !
And the turning capability was amazing - turned on a dime, and you could feel exactly what you did through the bar.
Price and durability is not really an issue - as with everything else, we go for the best, regardless of expenses.
And I found the LEI to be really really tough, even with everyday use.
Then the LEI's advanced to the next levels in the following years, and especially the big ones have remarkable turning characteristics (and therefore jumping and trick ability).
Turning a big foil by using brakes, slows it down, and reduces jump performance.
This is not an issue with the LEI's - and I really feel they accelerate much better when turning, than big foils (although the foils themeselves could be faster when going straight).
Starting and landing is also not an issue (only a thing that can contribute to the endless foil-LEI discussions...), as it is no problem with either type.
That you can start/land a foil straight in the powerzone or backwards, or alone - does it really matter ? Not for 99.9% of the kitesurfers...
Upwind performance was the same, or even better on LEI's when sheeted out.
So you asked what to expect, and above was what I experienced when changing.
Now the foils are much better, but because they have no advantages when talking about my experiences above - I have absolutely no reasons to change back.
The foils were more FUN just to fly, on land in light wind particulary - but when talking water use, the LEI's are just so much more suitable, AND performing.
Changing from foil to LEI:
You should expect to get a kite that is easier to jump, performs the same, and has heaps of hangtime, and you dont have to worry about water relaunchability any more, or getting the kite soaked.
You'll have to get used to spending longer time when relaunching from the water, if the kite ends up straight downwind.
And landing without a helper can in some cases only be done with the safety leash, if you are not too experienced.
If you get a big kite, you'll probably also find it very "heavy" in light winds.
And this is true. With insufficient winds, they can be quite problematic to fly.
But when powered for "normal" water use, they fly excellent.
You'll have to spend a few minutes pumping the kite.
But you get rid of any bridle tangling/damage or sea weed problems (bridles and sea weed - aaaaaargh
)
Some prefer foils because they like the characteristics of these, or are using foils for buggying.
But above is my description of what you should expect when changing