I have never liked the weight penalty being concentrated at the rear wheel, but they do work very well.
Have you ever rode a bicycle equipped with a Rohloff hub. It is a minuscule amount of weight and when equipped with a belt you get rid of the chain and derailleurs and all the maintenance, cleaning and adjusting of those parts. It is much more durable and reliable than a derailleur system. Serious world explorers use the Rohloff hub.