Dave, you ask about twinskins - I can not comment on those, as I have never seen anyone using these.
A few in here got these, so they might be able to answer, as I would expect them to behave relatively similar, but maybe not in all aspects...
But regarding small singleskin kites, ie Flysurfer Peak4 and Conceptair Firefly, the benefits are:
1. Way faster to set up and go ride.
2. No pump needed, just go "anywhere" with your kite and board under your arm, you dont leave anýthing on the beach.
3. They pivot turn REALLY fast, no LEI can follow (slyde is wrong here, sorry to say), so can be tossed around in every way you like, more options and more fun.
4. They can accelerate both when flown down and up (up, a small LEI can not), so you get more powerspike for a longer time, and you can stop the spike whenever you want if needed.
5. They drift WAY better than any LEI wave kite, so you can ride towards them for fun in flat water, and in waves, nothing comes close to their abilites.
6. They dont drop if wind goes almost fully away, can be kept in the air in a few knots, and you can loop yourself ashore, or walk when into low water.
7. No punctures can occur.
8. Seems to ride well on shorter lines than LEIs, and still have all benefits - can be practical for some.
9. Lower cost.
10. Pack a lot smaller.
11. Can be launched and landed in LOT more difficult wind and spots.
12. A lot easier to get "foreigners" to take it down, if needed.
1. They dont float. If you hit the water, it can be relaunched most times when done immediately - but if it goes wrong, you are toast and have to either pack it down (easy as small), or put it on its back and relaunch.
2. Less "sweet spot" silent range than a LEI, eventhough the actual wind range is the same or bigger.
3. None - cant think of more downsides?
A Peak4 and a LEI in the small ones goes about the same upwind angle, no difference; a double skin foilkite will go better upwind but doesnt matter for freeride/waves.
I bought my first Peak4 in late April 2020, and other sizes later, and can see from my log I have been out 120 wave/freeride kitefoil sessions with these kites, till now.
Out of total 296 sessions/sizes since that date - the rest on waveboards and wingfoil, or with bigger kites on freeride kitefoils.
Only used a LEI once instead, since then, a 10 onestrut because it could carry a strutcamera on an amazing indian summer.
A handful of times my 12 m2 strutless LEI.
The 12 because it is the only thing I have which can ride in 7 knots without feeling big like my 15 m2 foilkite (use that for 5-7 knots).
So in reality, I havent needed/wanted to use a LEI kite for freeride hydrofoil ever since the small single skin kites
The reason I took my onestrut LEI once - was to see this amazing colour of the water from above, in late august her in Denmark: