It's old technology. I had one on my secondhand school bike, and it survived its six years of 2 x 17 kilometer a day without giving any trouble. [>100 mile a week, 40 weeks a year, times 6, equals 24,000 miles].

It may take some time, indeed, to know how to shift down instinctively.

I mainly used it in the biggest gear though, the lower one was there to get me going after a stop at a traffic light, and as a home comer on the really windy days.