Seems like it's the thinnest guitar pickup there is, and it is probably true, among those commercially available at major dealers and resellers.
I have used it to expand the tonal palette of a so-called silent guitar, a Yamaha SLG-200S, after having tried a couple of other pickups that were not slim enough to fit under the strings at the fretboard's edge. Then I've installed it onto a 1959 archtop acoustic that needed a pickup, but had done nothing wrong to deserve a big hole across the top.
I glued it in place with double-sticking foam of the bathroom mirror variety, just a tiny patch in each corner (or you won't take it away ever again).
Finish is flawless, it makes for a perfect mirror suitable to shaving your beard in the morning.
Cable is really of superior quality, wish a number of other pickup manufacturers used something even half as good, for a change.
Connector is functional, nothing to dream at night, but it does the job, and allows you to plug and play without having to warm your soldering iron just for a quick listen.
Keep in mind that magnetic pickups do work on the magnetic principle, which might sound obvious at first, but that's not often the case.
While it's pretty clear that nylon strings won't make a mag pickup produce any sound at all, not too many guitarists seem to be aware that acoustic guitar strings (in either bronze, or phosphor bronze variety) are something else than nickel, nickel-plated or stainless steel electric guitar strings, from a magnetic pickup perspective.
In this light, don't be surprised if you'll hear a greater output on B and E plain strings, if they are the only steel ones in an acoustic guitar bronze stringset.
My Yamaha SLG-200S with Thomastik-Infeld BeBop roundwounds scaled .014-.055 can be tuned B-B standard, with enough tension to suit my taste, and the National Resophonic Slimline Pickup provides a really round, warm, full-bodied tone down to the low-B with great string-to-string balance, and a pleasant roll-off of high frequencies that I tend to associate to a classic humbucker (which, technically it is).
Great results with Elixir Strings for Electric guitar .012-.052, too, which are installed on my 1959 Framus Stella archtop: great tone, great balance across all strings, and a deep, full-bodied tone that retains the whole acoustic character of the instrument, with a rich, detailed dynamic contrast in response to touch and choice of pick, or nail, position.
Given the amount of design that went into this pickup, in order to make it sound like a full-sized one despite its thinness, and the superior craftmanship with which it's been built (and mirror-polished), the price is perfectly justified, and I'm happy, happier, happiest to have installed it.