There’s not much to say about umbrella adapters or brackets. Their job is simply to attach an umbrella and a flash to a light stand. In practice, there are basically 2 popular variants, the Manfrotto 026B and a cheaper resin/plastic alternative that’s sold under a number of brands (like this Impact one).
Though it’s more on the pricier side than its plastic counterparts are, the Manfrotto 026B is entirely metal, including the tilt handle. The only two plastic parts are the umbrella lock screw and the stand attachment nob.
The umbrella hole is large enough to handle umbrellas with a 9mm shaft and has one side squared off to prevent the umbrella from rotating once it’s secured. Additionally, the large rotation lock lever rotates so it can be positioned at any angle necessary.
On every sample, I’ve had the screw ends for both the stand and flash studs are rounded over so they don’t mark/dig into the brass studs as many of the cheaper ones I’ve used have.
The final nice touch with the Manfrotto 026B is the inclusion of a pair of brass studs with 1/4-20 and 3/8-16 threaded ends (one with two male threads, and one with 2 female threaded holes). I’ve found that these come in handy quite often when I want to mount something that didn’t come with provided 5/8” studs; for example my Really Right Stuff Flash QR clamps, my Lastolite EzBox Hotshoe, or even in a pinch, a microphone on small ballhead.