They will work. My first brew was a Mr. Beer kit and it came with 8 32oz plastic bottles. I would try to get brown rootbeer bottles for light protection. Also there ar some olhbs that sell new caps for them.
I thoroughly cleaned a 20oz Vitamin Water bottle once, and used it for homebrew. The pressure of the CO2 made the bottle and cap swell, but it was fully carbonated. The only problem was that the beer had a very distinct fruit punch flavor. Somehow the carbonation process had pulled trace flavors out of the plastic... Which made me think that maybe it was pulling out chemicals as well... So now I stick to EZ-tops
I have been considering doing this recently. I am a huge baseball fan, and the Rangers let you bring your own food and drink to the game, as long as it's not in glass and it's not alcohol. But I could bottle a bunch in soda bottles, call it "root" beer, and bring in a cooler full to the game. Sure as hell beats the $5.50 per cup of Widmer Hefe or Sam Adams (the best beer I can find at the ballpark).
Any of you Rockies fans can do the same thing. Not sure how many other parks let you brink your own food and beverage.