I've been struggling to keep my beloved Griffin PowerMate(s) operational; the company is still selling them new, both USB and BlueTooth, but spent about tree fiddy on software development.
The original software for OS X, v2.1, still mostly works, and offers, e.g., vastly better volume control (variable, precise; as opposed to percentage-clicks), but no longer controls certain aspects properly, and it prevents the computer from going into Display Sleep or System Sleep when running and the PowerMate is connected.
The old software doesn't support the Bluetooth models; you cannot run both versions simultaneously.
The new versions offered by Griffin are a joke; the controls are rough, flakey and extremely limited, and it only supports a single PowerMate.
And, of course, they are 32bit, so my time is limited to keep these devices operational without support.
I can arrange to provide you with one if that would encourage you to add this to BTT; I can assist in defining what makes the original so great and what features/functions it should support.
Griffin PowerMate USB and Bluetooth
Type of Mac: All
macOS version: Sierra and higher
BetterTouchTool version: 2.5