I know people would say - why not just use an ipad or an iphone but the problem with those things is that they have so many other things that you can do on them that they are distracting. This just does music, has a great sequencer, great if somewhat dated sounds...and you can dump the midi data to a computer and use it in a daw.....you can also sequence external synths and drum machines.
Thom Yorke, Bjork, Jah Wobble, Tricky, and PJ Harvey used these things quite a bit back in the day. KInd of a gameboy of sequencing. Runs on batteries. Very cheap if you have patience and can restrain yourself from using BIN.

Here is Bjork performing with an earlier iteration of the 70, the QY20 which was also used pretty extensively by Jah Wobble, Tricky, and PJ Harvey.

Thom Yorke with the QY70.

Here is a guy using one with a midi controller.
[youtube]http://www.youtube.com/watch?v=zga7X1yewfA[/youtube]
Here is a guy circuit bending the earliest qy, the qy10.





