Usage of the idiom like gangbusters has become a little weird over the years. Originally it meant with great initial excitement, speedily, with a strong start, or with immediate success. The idiom originally came from the midcentury American radio program Gang Busters, which began each episode with great excitement and vigor (i.e., with lots of loud sound effects). You can hear some episodes here.
But in the years since the show went off the air, the meaning of like gangbusters has become confused. A few writers still use it with its original meaning (i.e., with a strong start, etc.)—for example:
The G-Men started off like gangbusters and ended the game just as strong. [The Epoch Times]
Moore came out like gangbusters with three pull-up jumpers to get the Lynx off and running. [USA Today]
The episode starts off like gangbusters. [AV Club]
But over the years writers have extended like gangbusters to mean, simply, very well, not necessarily in reference to the beginning or early stages of something. It’s much easier to find instances of this usage, such as these:
China is growing like gangbusters. [Business Insider]
So while the iPad also sells like gangbusters, it’s not cannibalizing the Kindle as much as is excessively prophesized. [PC World]
This might have worked when the city was growing like gangbusters, and ever-increasing income was flowing in. [Naperville Sun]
It might be nice if we could preserve the idiom in its original sense, but the original reference point is now long gone. Already the idiom itself is mysterious to many English speakers and has taken on an old-fashioned ring, so its survival as a living part of the idiom is perhaps doubtful.