I think someone needs to RDWHAHB.
Oh man, I hope I didn't miss a good hot headed response before it got deleted?
This is a hobby, not academia. We can debate about theory all day, but on this forum anecdotal experience is worth a lot.
Just that when people use anecdotal evidence to reject something theorectical, that is a bit much, and should be pointed out. I can promise that I could set up a system with push-ins, correctly; make it foam; and then correct it with standard fittings. Especially if I used a push-in 90 somewhere. Dealing with cider and soda is a different ball game.
Also, some of this was after the OP already posted that his buddy had leaking issues with the push-ins, and didn't want to use them.
And while we're on anecdotes, since you're a big believer in them, does that mean you want in on the group buy for my Uncle Billy's "Lightnin' Stoppin' Sticks", too?
If I'd known about the John Guest fittings when I set up my keezer, I would be using them.
Even if you knew about the leaking and cleaning?
If these were listed, just like the barrier tubing being a ***** (for some people) to get onto barbs is every time the tubing is brought up, that would be fair. These are being touted as the great white plastic hope. I even see guys trying to use these for CO2, which should definitely be avoided, or at least properly warned against.
I check in very regularly in the bottling/kegging subforum where many people complain about foamy pours and many people help them solve the problem. I've never seen any posts about foaming problems with the fittings. If they cause such problems, those problems are rare.
The penetration isn't that great for these yet. Plus, many people 'resolve' their problems by carbing lower next time. Plenty of people give up when that works.
The original guy to mention push-ins recommended a union 90. Those have one of the highest risks of causing foaming, especially at higher pressures or with marginally balanced systems. They are a 'hard' 90, and add 2 additional joints.
I do think that 99% of the "help I have foam" posts are made by those new to kegging, and the problem is almost always line length, overcarbonation or temperature stratification. Occasionally something more fun like a bad o-ring, debris in a faucet or a bum Sanke coupler. It seems that barrier tubing and fancy fittings are mostly used by the more experienced keggers, who have already learned how to solve or avoid foaming problems.
Things change once you step up to soda pressures. Most of those threads don't have a happy ending. I actually think that vinyl might work better for soda pressure, because of the shorter length. There is the plastic taste, though.
Being this thread is about getting barbs into barrier tubing, coming in and talking about push-ins, and especially merely repeating your own anecdotal experience in support of them, would be like someone going in to a push-ins thread and telling them to quit being pansies and learn how to use tools like a man. Or, maybe going in to a barrier tubing thread and saying you don't taste any plastic in your beers, so quit bitching.
Also, there are many newbies who want to be like the cagey veterans, as in this thread by the kegging rookie who is planning on push-ins and barrier tubing.