As long as the sobe bottles are no longer glass, that should be fine. Just remember though, those bottles are not intended for pressure, so they may or may not seal well enough to hold that pressure back. Soda bottles can usually withstand close to 100 psi if I remember correctly.
What size is your tank?
I run a 20 oz bottle on my 7.5 gallon bow which was a sufficient amount until I started dosing ferts more regularly and at a higher concentration. I also have a lighting issue that I am trying to sort out.
My 8" cube has a 12.5 oz bottle on it and can handle the increased dosing schedule.
Both produce fairly steady CO2 output for about two and a half weeks. They have produced for over three weeks when the apartment is really cool and I get too busy. The smaller surface area results in lower off gassing rates, so it produces for a little bit longer.
I usually feel kind of guilty using the quick reply... my replies are rarely quick.