Safe or not, any kind of growth, even the kalm / kahm yeast creeps me out. For smaller batches, I've found a good method us using the ball jars with a thick mash and about a tablespoon of salt on top, leaving about 3/4 inch of head space. Then plastic wrap over the top, secured with the ring lid (and not the insert).
That said, I have been wanting to do bigger and bigger batches, so I went to my local brew / wine hobby store and picked up a few (3) gallon carboys, with the rubber stopper and glass airlocks. Easy to clean, easy to sanitize in the oven and life is great. I have two batches going right now. One of them is so active, I am noting 2 bubbles per second on the airlock. Its hypnotic watching it. I don't want to move them right now as they are quite heavy, but when I do, I will post pics in my long running thread.