A boost bottle or crossover tube are there to catch the small amount of blow-by passed the reeds and preventing it going through the carb the wrong way. A boost bottle has more volume than the crossover tube and therefore supposedly better.
The reason they do nothing but destroy your intakes is that any air-fuel mix that gets in there is sucked out immediately by the other cylinder, so the bigger size makes no difference to performance.
Boost bottles work on a singe cylinder, but will only get in the way and give you grief on a banshee. :cool: