If you decide to manually "shake" a better bottle, it is recommended by the manufacturers that you use a tennis ball on the bottom of it. This helps prevent cracking of it due to flexing of the liquid in the bottle.
From the website;
Important Note: Never rock or swirl Better-Bottle carboys without using a tennis ball. Doing so will cause the edges of the bottom of the carboy to flex under great stress repeatedly and eventually cause cracks, like bending a paper clip back and forth.
There's been a few threads about it. They are a great product, but if they get oscillating there can be problems.
There's no point in contacting them, they already know.....
Like my snazzy new avatar? Get Sons of Zymurgy swag, here, and brew with the best.
Revvy's one of the cool reverends. He has a Harley and a t-shirt that says on the back "If you can read this, the bitch was Raptured. - Madman
I gotta tell ya, just between us girls, that Revvy is HOT. Very tall, gorgeous grey hair and a terrific smile. He's very good looking in person, with a charismatic personality... he drives like a ****ing maniac! - YooperBrew