It's an OK wireless handheld microphone. They sound OK for speech and similar, could probably work for karaoke and less professional usages. Feels a bit plasticy, so handle with care.
Not stackable, nor mountable in rack.
Beware, that this device is prone to receiving static signals from nowhere, when the transmitter is turned off. When used for anything, be sure to have the mixer close by to mute any channels using these wireless mics, otherwise there is a slight risk of loud static noise in your speakers.
To summarize, OK wireless mic for less professional usage. Perfect for newcomers, to try out wireless technology (due to price).