Frequency Response: 20Hz-20KHz
Connector: Gold-plated L-plug
Warranty: 1 year
The M4 comes in an attractive package similar to the B2. The accessories included are 3 pairs of silicone eartips, a pair of Comply foam eartips, a shirt clip, and a hard zipper shell carrying case. It's a fair amount of accessories for the price you pay.
The M4 fits comfortably with no problems. I was able to wear it for long periods of time without discomfort. Isolation is pretty good for a vented IEM but not the best. The design is very similar to the Xcape IE except for the vents at each end. It's pretty easy on the eyes and not flashy at all.
The M4 has a solid build with its metal housing and don't see it falling apart very easily. The cable is a little stiff, lacks a chin slider but doesn't tangle at all and is pretty easy to handle. It has all the proper strain reliefs. There's also a remote/mic version available.
The M4 has a treble and bass emphasized sound overall. Treble is detailed but can get harsh with certain tracks. Midrange is slightly recessed but pretty clear. Bass is punchy and has a good rumble to it. It's has a fun, musical sound that would do well with many genres of music.
The M4 is a pretty good buy for the price. It has a fun, detailed sound with a good amount of bass and a slightly recessed midrange. It would do well with musical tracks more than it would with vocals. I'd recommend it for those wanting a nice sounding IEM with a solid build and comfort. It can be purchased for around $55 right now @ mp4nation.