I have the Shimano RevoShift SL-RS35's on my comfort hybrid errand bike. They work fine. Shifting isn't as precise as my mountain bike's indexed thumbies, or road bike shifters, but good enough for casual rides and errands.

The SL-RS35's aren't serviceable, other than replacing the cable, so I've had to replace one when the original cracked after about 8 years. It's mostly plastic including the ratcheting system so when the plastic outer ring cracked and wouldn't hold in gear I just replaced the whole thing. The other original shifter is still good after almost 10 years.

And I bought a complete spare set of both shifters and cables for only $10. Only problem with the replacement kit is the included cables are a bit short for my long wheelbase comfort hybrid. But I also have longer spare cables around so it's no big deal. I can use the shorter cables on another bike.

And for most bikes this won't be a problem if you buy the complete RevoShift kit. There are a few comfort hybrids and cargo bikes with unusually long wheelbases, tall riser stems and handlebars that might require longer cables.