The best bee feeder ever made as an open feeder. This is in the playlist for this feeder.

So, as far as safe for the bees, ease of use, 2 minor modifications and flexibility as to feeding rates. I personally claim that this is the best and only bee feeder you will ever need. I put this video in a playlist so you can get a more thorough overview of this old School feeder available from Dadant and I think Mann-Lake makes one too.