Well friction is an issue depending on how much one’s skin can take. I seem to be really sensitive, and the less friction the better, even if this means that I have to be very careful in every jelq so that my hand doesn’t slip off the shaft.
Having some friction, more or less friction, is really up to how much your skin can take. I have already developed some discoloration with dry jelqing (and I am not even in my second month yet) and as I can see my skin is fine with the less friction I can have. I go with that, smaller gains? Oh , well, better slow than damaged.
Just my newbie opinion (I must put that in my signature so I don’t have to type this all the time :-) )