I have one for my siphon—filters the grinds perfectly well, but as others have touched upon, it's a bit of a chore to keep clean. In addition to cleaning after each use, I boil the crap out of it every now and then for extra measure with a touch of vinegar and it seems to keep it clean.
I still use paper filters for my v60 and I've never used the coffee sock on it. Maybe I'll give it a try.
That's a valid point. For me, I use my siphon sparingly nowadays (maybe once a month), so it ends up being every time I use it. So, in the grand scheme of things, not much I think. When I was using the siphon more often (maybe 3 or 4 times a week) I would boil it at the end of the week—much higher impact for sure.
If I were going to plan this out a little more for my current routine/usage, I could boil it inside my kettle when I do my monthly descaling, but that might degrade the cloth much faster.