I use the Lens Coat Covers for my 200/300/400/200-400 & 600.
I shoot Wildlife mostly, Africa & Arctic/Antarctica, these can be harsh Climates & Conditions on equipment, the Covers offer some protection against Dust/Dirt/Snow etc, plus the occasional bump & scrape situation.
But the main reason I use the Covers is to assist in "resale value", I've sold Version 1 300f/2.8 & 400f/2.8 Lenses after 2 years of use for the same price I originally purchased and in both cases having Lens Coat Covers have been a deciding factor from the point of view of the buyer, the Lenses not only are in pristine condition, but they give a clear message to the buyer that the previous Owner cared enough about his gear to protect it.
Some modifications are necessary though with the lens Coat Covers, you need to use a Box Cutter and remove the plastic windows so you can access controls when needed, you also need to cut a Box into the Cover to access the Drop in Filter, The big whites are weather sealed so the Covers less about water.dust getting in, and more about offering protection against scratches etc.
That all converts to $$$ for me, I cant comment on the "Lens Skins", until this thread I'de never heard of them, but i may now look at using something like this on my 70-200f/2.8 II, seems like a good idea to me.
Ultimately it's like a Car Cover, or Painting a house, you have a reasonable Investment tied up in Lenses, in my own case, Big Whites, +/- $50k, Lens Coat Covers for these Lenses cost +/-$450.00 If that helps protect the gear for ultimate resale at a best price, it's a sound investment.