Excellent kit for fixing some vacuum leaks when replacing a motor. Some of them are a little clumsy, but they get the job done. It's also nice to have on hand.
That's what you'd expect in a vacuum cap but for the price I think you're paying for the Holley brand name. I saw the same vacuum caps in the port. Freight after I bought them for half the price of the same quality!
I used one of the 1999 Mazda Miata cruise control remover plugs to unplug the CC vacuum port on the intake manifold. It stays tight and seals. Seems to be a good quality rubber/material, time will tell how well they hold up.