i used four waterless locks on my flex tanks during secondary ferment...and i did worry but it was all for naught....afterwards i used the floating skin....all went well
for my new tanks however i decided against purchasing flex tanks waterless air locks and went to home depot and got a 3/4 inch threaded adapter w a space on the other side to accept a rubber bung w the typical water filled air lock....cost....77 cts each
something in my gut says that a waterless airlock is an accident waiting to happen ..if for instance a fruit fly were to find its way to the point where the ball meets the airlock seat and or a piece of dust were to sit there, then you could have an opening that you would never see