I've never tried the Zymox cleaner, just the actual antifungal/antibacterial drops.
A lot of people really like the BioGroom shampoo. The cleaner would be worth a try. I smelled the shampoo once though and the scent was so close to Skin So Soft. I'm not a fan, so the stuff doesn't come near my girl. I'm so picky that when talking about a medicated shampoo or cleaner, I'll have the vet open and smell first to make sure it's not gross.
Even if the ears look okay, it's never a bad idea for them to swab and see what they get if anything. If they are getting something, then cytology is needed since there is a smell.