I got to try the "mushroom" today. It didn't work for me. I couldn't grip it well enough with my toes. The nice thing was I could just ignore it and try riding strapless. It went OK for me. I found the balance point where I could hold the board most easily (though still difficult) and then concentrate on getting the kite positioned properly. I had trouble getting up on the board and pointing it downwind flat. It kept wanting to be on it's side too much and I would just fall over it. Once I got up, I was able to make plenty of good long foiling runs with pretty good control of ride height and direction. Maybe a chance for more practice tomorrow. It worked well enough without straps that I will continue this way for now at least. I guess my newly purchased foot hooks will sit on the shelf for now.
What size of kite ?
I have the opposite experience - that it will NOT keep itself on its side, when using big kites - as the downstroke powerburst takes so long, that the board/foil will drop to upright, where it is impossible to start strapless.
Too much on its side only seems to be a problem if powered so you get up quickly and with power (like if using smaller kites maybe less than 10m2, or if using a big size relative to the wind).
The good thing when on its side, is that you will learn extremely fast how to handle this - as you simply got too much power in the kite at the wrong moment, and this can be very easy compensated
If the board is pointed too much downwind, and flat, you WILL fall forward and over when trying to start.
So the difficulty is to keep the board on its side, and not too much downwind, when strapless.
Whereas strapped, you can do almost whatever you want
At least my experiences with a surfboard/hydrofoil.