I've only heard this hardener-makes-washing-difficult argument on paper, not film. Even then, photographers have been using Kodak Professional Fixer (the powder kind) that contains hardener for decades.
I do know, if you intend to tone, hardener impacts toner's ability to change color.
Also, when you use 2-bath method, length of fixing total is not any longer than one bath method. I wouldn't think it'll make that much difference. I guess a better question will be, do you use a kind of film that require hardening treatment? Most modern emulsions are hard enough that something like that isn't even necessary.