Bean Animal drains not draining properly

[fishytime]

please forgive my ignorance but......whats the advantage of the Bean overflow over the Herbie?......Ive never used one, nor do I think Ive ever seen one being used on anybodies system that Ive seen.....seems like quite a lot of extra expense (two gate valves and three bulkheads versus one gate and two bulkheads) and fiddling around with the Bean......