there wont be much latency as long as using the right audio driver/soundcard, reasonable comp spec etc.
i have been using it with ableton, sonar etc running various vsti, using asio4all when not using my audio interface and its audio driver. The latency is around 12 to 15ms after tweaking the buffer size, its pretty much unnoticeble for me, even if randomly banging on the thing at fast speed. With audio interface connected, it can get even lower.
Quality wise, the way which the key are connected on the nano itself, is a weak point, imho. Have already 2-3 keys falling out/broken from my first nanokeys(even after fixing it the keys manually back, the feel and velocity kind changes a bit to less sensitive. Underneath the key is a small rubber padding thingy which need to be put at correct angle, if not the sensitivity/velocity of the keys will be affected coz it aint getting good contact with the circuit board contact point beneath the rubber pad) where some of the keys came off after a while, due to the tiny clip thats holding the keys plus the angle of pressing which will affect the position of the keys after a while.
If wanna use it intensively, it might not hold up to it. If just wanna get a basic idea of melody using it to run vsti and bulk of the work is using piano roll screen within your daw and manually drawing the midi notes, it should be fine.
If wanna play with it more instead of drawing midi notes, i would suggest the akai lpk25 midi controller. Its built is much better, sturdy and the real keys(even though its of smaller size, similar to the microkorg size keys) is much better to play then the nanokey, which feel more like a loose computer keyboard.
i have move thru 2 nanokey set and now using the akai lpk 25. For the keys wise, i prefer akai. I love the other 2 nano gadget though, nanopad and nanoknotrol.
anyway, heres a pic for comparison of the size of nanokey and lpk25. Just incase anyone is wondering how big difference between both in term of size.