You want Model A; seems to be around $29. everywhere. would vault for free shipping like Jegs, etc. Don't think I would buy used at eBay.
But, like every buy suggestion here: wait on a concensus

Thanks, Richard I watched one sell on E-bay for over $100 a few days ago and had to scratch my head when I've seen them for around thirty, like you said. Might have been a rare model or something that was more unique than the usual models. I used one years ago on an MGB's SU carbs and it worked slick. Terry

Can use an 'old timers' method by getting a rubber fuel hose. Hold it at the carb throat (do at same location on both carbs) and insert other end in your ear. Air cleaner off.
Adjust carbs where the pitch and volume of the air flow is the same at each carb.
So I have been told.

I have a uni-syn that I bought more than 40 years ago for my MGA . The instruction sheet has Edelbrock Corp., El Segundo Calif. The new ones I have seen on ebay are made in China of course and probable work just as well. But when you see a high priced one it is most likely old and US made.