I caught a bit of the Red-Thing bug when I got some of Woodpeckers' tools at a garage sale-for half retail price since they were used. I was inspired to consider other Woodpeckers tools, and the In-Dexable combination square seemed to offer enough innovation in it that I plunked down the $170 (gulp) and bought the regular (non-XL) 12" version.

(I also bought a spare 6" blade-but I wish I hadn't. The head of the combination square is just too big (it's normal-sized) for such a short blade, so I'll just use the 6" one on its own I think.)

Manufacturing fit and finish on the combination square is superb. The engraved scales and numbers are lighter than I'd like-I'd prefer more contrast and visibility-but it's fine. They say they're "crisp and dark" but I'd say they're crisp and not-dark.

The blade is wider (1-1/2") than most combination squares, but I don't know if that's good or bad-just something to consider if you're buying one. It's also actually 12-3/8" long. Oddly, the blade feels thinner because it's wider (weird, right?) but it is 2.25 mm-just like my "real" combination square!
The adjustment knob is beefy, perfectly grippy, fast, and comfortable between the fingers. The barrel is rounded on the edges-a great detail.

Its accuracy is perfect for woodworking and as good as any other square I own, engineer's or otherwise.

The two features that really make this square unique are the In-Dexable pin which definitively registers the head at one-whole-inch increments and the slide-out shoulder on the head.

The slide-out shoulder is perfect. It's almost a rubberized-gasket feeling to slide it out and back-stiff, but not too stiff. Intentional. The toothing on the shoulder, which your thumb pushes against-is aggressively toothed and your thumb won't slip off it… ever. It's a nice feature to have so that you don't have to hold the square perpendicular to your work and is helpful.

The In-Dexable pin is… almost worthless and actually distracting. [8/16/21-see update in my comment below regarding this] It's almost making me want to return it. When the head is loosened the pin continues to stick out just enough that it slides/scratches across the blade, and ever-so-slightly catches on it every whole-inch. As you zoom up and down it click-clickety-clicks every whole inch. It's not a full-on-grab (most of the time), mind you, but it's a clickety-hiccup sometimes that just detracts from the smoothness. And sometimes it does grab one of the index holes when you don't want it to-and that's just not right.
It seems like the In-Dexable pin should fully retract with a spring until you WANT to use it. How lovely it'd be if it had some of the same resistance that the slide-out shoulder had, if that was possible. There-by intention-when you WANT/NEED to use it, but totally out of the way when you don't. It does seem like there's a spring in there, but it's the world's weakest spring.

One other odd thing is this: I'm designing some new storage of my tool wall and using magnets for a variety of purposes. The stainless steel blade is almost non-magnetic (I've emailed Woodpeckers to ask about this). Yes, the blade is full of holes and is thinner than most of the other combination squares-but my strongest magnets barely stick to it. They stick, but barely. [8/16/21-Woodpeckers says this to me in response to my inquiry: "We use 301 stainless for these blades. 301 has a high nickel content and is considered austenitic (non magnetic) in its annealed state. It can become magnetic through a cold working process that we do not use."]

My order came with a metal bracket for wall-mounting it-something I didn't expect and was a nice surprise.

Everyone reading this is going to comment about Starrett squares-I know-I've been here long enough. Good on you. I bought this one, and I'm quite happy with it except for those quibbles above. Maybe I got a bum-one, maybe my complaints won't be yours-but I thought I'd share my experience with a $170 combination square purchase, and hope it helps you as you consider your needs!

[10/12/21 Update: After using this for a number of weeks I've really found that the laser-etched numbers reflect the light and aren't as dark as I need them to be. I emailed Woodpeckers and they sent me a replacement ruler with slightly darker numbers/lines. Kudos to them for great service-though I'd still like the etchings even darker.]