And yes PETG will shatter. Disk shot modded with handyman. Shattered barrel almost in perfect circle and blew it out of the gun on the first shot. Launched the barrel with dart still in about 15 ft. I've had it also crack from pressure put on it. And twisting it will also have the possiblity of cracking it. All about too much too fast and possibly a weak point in the tube.
Maybe I misunderstood him and you misunderstand what shatter means. Glass shatters. PETG can crack and break, but it won't shatter. If something breaks in a perfect circle, that isn't shattered, it is broken/cracked.
Anywho...it doesn't depend a lot on what you are doing with it. 9/16ths brass and thick-walled PETG are a similar size, so what you're doing with it matters a lot. I am currently working on a new take of shotgun titan, and I will have either four or five barrels, so brass would cost ~$6, and PETG would be $6 even if I only ordered the few feet I needed, so the PETG is definitely cheaper. I also am working on a new longshot with a different take on...everything except for the breech. The breech will be an Angel style one, which would be impossible to completely replicate with PETG.