Not entirely Jimny related....

This One?

Saw that last week myself.

Its just as dangerous as any other lifting or recovery equipment, its how it's used rather than the device itself. Now that as a statement has just opened up a range of activities from perfectly safe to suicidal. So many factors, so many opinions, this is just mine
So it has a place, just use it safely.
I like it as a DIY solution if you want one.
 

In principal it looks like a good idea if you favour the trolley jack away from paved or concrete surfaces.
its going to work better than wheels on any surface that's not solid, spreading the load over a larger area. Its possibly even easier to slide underneath, and may even slide with the arc as it lifts. This does depend upon the surface it's deployed and how much grip the vehicle has on terra firma.
I can see the principal for it's existence, so even if it is an April Fool, under certain circumstances it's a good idea.

But then you can sort of achieve the same with some sand boards / and a normal trolly jack. 

Using a normal trolley jack on a piece of 18mm plywood would be better in every situation I can think of.

whats wrong with the standard screw thread 2ton that comes in the back? if you need more height take some 2x4 short planks and the its a straight lift also so no worries about changing angles? am i missing something? or is this just a ooh shiny thing

The standard scissor jack is more than adequate to lift an axle enough to change a wheel and add a plywood based load spreader and you are covered for most, if not all, occasions when away from home. It's also lighter and cheaper than the skid jack mentioned.

Roger

If you had to jack on soft ground on a regular basis then I can see how this sled would be a good idea and if there is enough slip in the surface the jack would still move.

It's a lot of years since I have had to jack anywhere apart from at home and never on soft ground, so for flexibility a standard jack and a bit of plywood would be just as good and more versatile (it would slip on any surface) even if it does take slightly longer to deploy. You could always attach some handles to the plywood to make it easier to lift up after use.

standard practice is to attach a short length of a suitable rope to pull the ply. base out of it's hole.
This reminds me of the K.I.S.S principle.

Roger

Like most things it exists because it's slightly better, or fits individual circumstances better. 
The standard cheap sctew jack you get with the Jimny is fine for changing a wheel, but like many I own a trolley jack as I find it physically easier to use.
So at home the trolley jack gets used for everything, never the supplied screw jack. 
So, hypothetically speaking, if I was in a position that involves a lot of jacking away from home then I could be persuaded keep a trolley jack in the vehicle. Now add soft ground and a dislike of thick planks on which to balance any jack, hey presto, I am in the market for said skid jack. 

Perfect example of why the standard jack is no good for me - - - - hypothetically. 

But then none of this applies, which is why I have only ever used the standard screw jack to change a wheel out and about and why it's just as good. - - - but then I did wish I had my trolley jack on me when I did it