First impressions, all good...
Bought a pack of 6, received 7!
At first, I thought the backing had come off, but then realised those were little (non-adhesive) packers! Ha Ha!
Both the filters and the backing are very thin, so good nails required to peel off the backing.
Everything else is great. Stuck well. Fit well. Easy to fit. No creases or bubbles.
Still let a little too much light through for the perfect result, but as that's A/ personal preference and B/ Down to my lack of experience with all things lens/light diffusing, I cannot fault the product or the seller for that. I maybe could have got darker ones to start with, but as I'm new to this, I'm happy to have followed the product description, and live by my decision.
To that effect, I'm just about to order another set (of the same) and double up on each lens. At least I'm confident a second layer of the same will almost certainly be perfect for our needs.