I keep thinking about this design...and see many disadvantages.
Large fittings are expensive.
I personally don't find $3.98 for a 4" street elbow to be all that expensive or expensive at all, but understand to some it might be... Also, based on the amount of feed I was wasting on the ground and around the other types of feeders, prior to using this feeder the elbow cost was easily negated in only a few short weeks time in saved feed cost...
http://www.lowes.com/pd/4-in-Dia-90-Degree-PVC-Sewer-Drain-Street-Elbow/3609606
Doesn't always eliminate billing out.
Based on personal experience I would beg to differ, if built properly even if it does not stop 100% of billing out it has for all intents eliminated nearly all billing out and I have yet to see a feeder design shown to that eliminate more billing out so it clearly wins in that category for me...
Head 'buried' in fitting leaves bird vulnerable to bullying.
Can't say I experience this... Rarely is every port on my feeders being used at once (but that could certainly vary by feed port to bird ratio, just like it does for water nipples) even in the morning the birds all come off from roost at different times and do different things, so there is not even a mad rush at first light to the feeder that I have observed... Maybe my mixed flock is unique but I have never observed any thing I would call bullying while they feed at least nothing more than normal chicken pecking order activity that would be happening at any type of feeder...
Only 1 bird at a time can feed per station.
Regardless of feeder type there is always going to be a limit to the number of birds that can eat at a single time with any feeder...
Biggest thing that bugs me tho is, container is never fully emptied, leaving stale and possibly moldy feed at bottom or extra work to empty and clean container on occasion.
For this I will fully beg to differ as false... My feeder if I let it go will be as empty as one would expect with just a little food in the corners, maybe a single cup or two total left in the entire feeder most of the bottom of the feeder is bare... Either way before I refill I simply tilt or shake the feeder and the small amount of feed left in the corners gets redistributed across the bottom to be eaten first with the new load, and since I fill it every 1-3 days, that left over feed hardly has a chance to get moldy or stale... Also being in a mostly enclosed container, there is no condensation, poop,rain or what not getting on the food and that helps greatly in eliminating spoiled food...
I do understand it might not be for everyone, but based on my hands on experience with multiple types of feeders, this one has come out on top with nothing else I have tried being close...