I've not seen/heard of one of that brand, sure would like to see it.
In general auxiliary transmissions are good and neat things. Take a little effort to install properly but not tricky.
Some are quite large, not suitable for a smaller truck, be sure it'll fit first.

•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-