My experience
I use a similar product, using red sliding aluminum blocks rather than the pipe-like pieces on the Slidedown. Same concept though. Might even be an earlier version. Anyway I carry them for use whenever local tiedowns aren't present, ropes are too short, I have to use ground anchors, etc.
If suitable ropes are present, I just use the supplied ropes, so that my civilization-preserving knot-tying skills are maintained.
Anyway:
1. Been very happy with them generally
2. Once in a while they are just a bit too short, especially for the tail. RVs are short airplanes.
3. The large-ish hooks that came attached to mine don't always fit in the tiedown rings embedded in the concrete at airports. I carry additional smaller hooks for this reason. Looks like the ones you pictured should work in most locations.
Since I never miss an occasion to harumph: it's surprising to me how much variation there is in the size and accessibility of embedded tie-down rings at airports, and how frequently rings are jammed with dirt, etc. I'm also amazed how often tiedown ropes provided at airports are completely shot. You would think liability concerns would encourage people to use fresh ropes. [/harumph].
I have used the Slidedown tie downs on my 14A for about three years now and I like them. They have held up well in Montana and Minnesota winds (30+ knots). My small nit is that they could be a touch longer for the places where the tie down rings are wide.