Know a few folks that have had or still have a gear vendors unit. The impression I get from them is it's a fine unit.... but it's not near as good as they claim it is. Main thing is it won't last holding back aginst the engine on a down hill.
Overall a good option if you understand the limitations.
Again I don't have first hand experience ...

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-