The AKG C391B is a thin cigar-like microphone that is part of the AKG Blue Line series. It comes in two parts; the microphone body (SE300B) and a cardioid capsule (CK91). The mic is designed for recording high frequency instruments and is traditionally used for hi-hats, cymbals and acoustic guitar.
The C391B is an incredibly high quality and very sensitive mic. It doesn't pick up much noise from the body of the microphone so you can hold it, although being so sensitive you probably wouldn't use it in a live situation. The mic overloads easily, especially if you're not using pop shield, but you can beatbox at 90o to the end of the mike at a distance of about 2" away and it picks up everything loud and clear. The mic also sounds great on the throat although like most condenser mics, when used on the throat you have to keep pretty still as any movement causes unwanted rustling sounds.
This mic would be a great choice if you want a high quality all-rounder that you will occasionally use for beatbox in a studio environment.