If you've never tried them, I recommend setting up a bike with some. I've never felt so in-tune with my friction shifting. As nice as ratchet friction is, there is play between each step of the ratchet. And most simplex retrofriction shifters are old and used enough at this point that they also have a tiny bit of play between the position that you pull to and the position that they relax into after letting go of the lever. The symmetric shifters I've used are resolute in their position, which I really like for friction. You move the lever, and there it goes exactly where you want. I found that I developed really accurate muscle memory for single, double, and triple shifts that I haven't been able to as easily with other friction shifters.

My only gripe is that they're hard to use with half-frame top tube bags.