I have recently bought a TDX-4 with a Center Mounted Leg Rest. (Reason I had to go with a center mounted was the limited legroom in my van that I drive.)

Well, as long as I don't tilt back or recline, my legs tend to stay on the foot rests just fine, soon as going into the recline position, feet keeps sliding off the plates.

I have heard some quads put a strap around the feet or place a Velcro underneath each shoe. Any other suggestion?

The center mounted legs rest is a solid concept except needs more refining. I think we need wider heal guards on each side of the footrests as well as support pads for calves.