Twist offs can be used, but they will sometimes not create an air-tight seal. If your seal is not air-tight, you'll never be able to get your beer to properly carbonate because, much like in your fermenter, the CO2 will simply escape the container. Unfortunately, I don't know of a good way to check whether your bottles will seal air-tight or not, and even though water or other fluid might not be able to escape, air may still be able to.