Look familiar?
The expensive version
the only real difference is the $ one has a diaphragm in between the pressurized air and the brake fluid. It keeps humidity out of the fluid. If you use new brake fluid every time you use the bleeder, that's not a factor.
He used a GM cap because it fit his master cylinder. We might need a MB cap. Cheap enough. Note that the GM cap had a small relief groove that he had to fill with RTV.
Enjoy,