The sound quality is sufficiently clear when recording, but is not sensitive enough to satisfy the most demanding users such as musicians or professional reporters. You need a relatively strong source.

Here's one MD player recorder that I know has the microphone jack and works great with this microphone:
'Sony MZ-NF810CK Net MD MiniDisc Recorder with Car Kit'

However, don't be fooled. Not every MD player has the appropriate Mic Jack. Double Check the technical documentation to make sure. Units that definitely do not have it are:
'Sony MZ-NE410 High Speed Net MD Walkman Recorder'

Notice the deceptive "Recorder" moniker in the product name. Don't be fooled! Very few MD "recorders" actually record with a microphone!

Not sure about these:
'Sony MZ-NF610 High Speed Net MD Walkman Recorder'
'Sony MZ-N510CK NetMD Walkman/Recorder with Car Kit'
'Sony MZ-N505 Net MD Walkman Player/Recorder'

Do your research before purchasing any MD player. All in all, this is a good value and the ideal microphone for those wanting to record onto a Sony MD.

Not JUST for Sony recorders (Rating: 5.00)
Review : Contrary to earlier review, this microphone works GREAT with devices other than Sony; just make sure that your recording device provides plug power. I use this microphone with my iRiver iHP-120 20GB MP3 Jukebox --- records great stereo sound directly into MP3s. Fantastic for recording my kids' concerts. Highly, highly recommended.

brilliant product, but only works with Sony products!! (Rating: 3.00)
Review : I fell in love with the design and spy-movie size of this microphone, but it doesn't work with most recording devices, because most recording devices aren't equipped for "plug-in power", eg, the Denon DAT player that I wanted to use- couldn't get any signal to record on this. Ditto for my friend who bought the same microphone to use with his laptop- couldn't get any signal. If you, like me, dig sony's products on the whole, you should get the ECMMS907. It takes a battery and will work with any recording device.