Definitely cant be starting with a double stack, you'll end up playing too tight and then get them all-in with A's and get busted .. and then no way back to take the add-on ..
However, this sort of structure it's worth keeping an eye open on the clock, if there's just 2 or 3 minutes left before the break and you have under the starting stack, I would then take the re-buy and go make a cup of tea, dont even look at the computer for that 2 or 3 minutes,(dont want to get busted now)..
Then at the break take the add-on if required giving you a decent stack for the main game proper (start then is a freezeout) ..
The other thing with only playing just the one starting stack is, it gives you a slight advantage for playing a few more wider range hands in position, without the 'scare' factor in the back of your mind..
Good luck us
