I usually mention the journals I'm reviewing for, as it can counts as a position of trust (i.e. to improve the quality of science).
My question is, how connected is the reputation of a journal someone is reviewing for, with that part of his/her CV. What effect would it have to the CV (and whoever reads it) adding low quality journals in the list of journals where the person is a reviewer? Would you consider it negative, neutral or positive?
I think that if they are only bad journals, the lack of good ones might be considered a bad thing, so avoiding mentioning the journals the person is a reviewer might be preferable.
If it's 1-2 in a list of a few respectable ones, then it would be neutral or even positive, as you try to improve the not respectable journals.