You'd have to worry about scratches on stainess too. On stainless to get rid of the scratch you'd have to polish it out if possible, if not it would be expensive to replace. I imagine that you could polish a scratch out of plastic too. But then what would you put in the fermenter that would scratch it?
Another thought I had was what about off flavors? Some people frement in plastic buckets, do they get off flavors? I use glass and have only done 5 gal batches, but was thinking of moving up to 10 gallon batches with in the next year or two. I have two glass carboys and could split a 10 gal batch into both of them. I've never read that glass can absorb flavors/aromas from the contents, but what about the plastic?
I like the idea of a conical, and not having to pay someone eles to configue it the way I want it would be a plus. Another plus would be the time savings of using it as a secondary too. Just open a waste valve on the bottom and drain the trub out.
Does anyone know someone who uses plastic conicals that can share some experience?