I don't understand how BB would seal better than glass - I have never had an issue with sealing as long as you use the correctly sized stoppers.
The seal between a stopper in a glass carboy is adequate for fermentation, but not for heavy handling. Gum rubber or white rubber stoppers will pop out of glass if subject to any amount of pressure and the red/orange rubber blow off caps leak. OTOH, a #10 gum rubber stopper crammed into a BB will not come out until you pry it out with your fingertips. Almost as good as a barrel bung
Why does this matter? For a couple reasons. First, when going to the orchard to get juice, the carboys are in the back of my truck for an hour each way. I often pick up cider for my friends so I have a mix of plastic and glass in the truck. The plastic carboys are never a problem. But the glass carboys are prone to having their bungs pop out during the trip. Its not a size problem, they just dont stick as well. After a few trips of arriving home with half the glass carboy bungs in the bed of the truck, I now put cellophane and a rubber band over the stoppers for glass carboys so that this doesnt happen. That is a PIA
Glass carboys are a PIA when going to the orchard for other reasons also. They need to sit in a milk crate for protection, so they dont pack as tight, and are a good 15lbs heavier than BB. The difference between 50lbs and 65lbs may not seem like much, but after loading 20+ carboys in and out of the truck, its a big difference. Every time I make a trip to the orchard I tell myself no more glass carboys because they are extra work. For some of my friends glass is all they have so I put up with it, but probably not for much longer.
Next - if I add honey or sugar to the cider before the pitch, I will put a gum rubber stopper back in the better bottle and then lay it on it side and roll it back and forth on the floor to dissolve the honey/sugar. I frequently do this with 4-6 carboys at a time, rolling them together on the floor. This is much, much easier and faster than any other way of dissolving sugar/honey and there is simply no way to do this with a glass carboy - no matter what stopper you use, it will pop out of glass if you lay the carboy on its side.
Finally, while cold crashing, a little pressure will often build in the carboy before the yeast shut down. With a gum stopper in a better bottle, this is no problem. With a glass carboy, the pressure will pop the stopper out.
During fermentation, I use the white rubber drilled stoppers. They dont seal as well as gum stoppers, but they seal plenty tight for fermentation and dont pick up any smells.
How could they [BBs] possibly be easier to clean than glass?
Well, for starters, they are light and unbreakable. When I clean my BBs, I rinse them out completely first. Then I put about a quart of 1-Step solution in each and slap in the gum rubber stoppers. Next I grab the carboys two at a time, by the neck and agitate them for about 2 minutes, which is twice the contact time required for sanitation. I swing them up and down like barbells, which is easy because they are so light and after 2 minutes of this, I have two completely clean carboys. Next, I let them drain into a clean pint glass, which I can set anywhere. Try doing this with glass. With this method, I can clean 8 carboys in 15 min with time to spare, and dry them in minimal space, with no special equipment. Agitating a glass carboy takes both hands and more effort. Because all of my glass carboys have carboy handles, drying them takes a special stand. Glass is easily twice the work to clean.
The fact that they [BBs] discolor shows that they are not being completed cleaned.
No, PET discolors slowly due to UV exposure. It is hard to notice unless you compare a 5 year old carboy with a brand new one.
So are you saying that it is harder to avoid oxidation with glass? This is simply not true.
No, what I was saying is that when I was a noob, I used all glass (which was the "conventional wisdom" of the time), and this did not prevent me from making the typical noob mistakes that result in oxidation. Now that my process is tighter, I see no difference in oxidation between glass and BB.
This [You have to be a little more careful when cleaning them] contadicts your first statement about them being easier to clean.
I should have been more specific - What I was referring to is that if rinsing does not wash out all the debris from a BB, and you need to use a bottle brush (which is rare) then you need to be careful only to let the bristles of the brush touch the BB and not let the metal end of the brush scrape the side of the BB. BBs are easier to scratch which is a con, but an avoidable one.
Your glass will be around for you to give to your sons and daughters in your will, the better bottle will not.
I am much more concerned about whether I will be able to keep doing this when I am 70 then what happens to my equipment when I am gone. At 50lbs for a full six gallon BB vs 65lbs for full six gallon glass carboy, I'll take BB any day. Having good looking brewing artifacts is nice, but I am more concerned about making good cider with minimum effort.
Preference doesn't and shouldn't overwhelm facts about each product type
I agree. Having used glass for over 15 years and BBs for the past 5 years, and seeing first-hand how they perform side by side over hundreds of batches of cider, I can say based on experience that the BBs are much easier to work with and perform just as well.
If you want to use glass, that is fine, but dont confuse 2nd hand talking points about the supposed superiority of glass with "facts" about which is better.