We have been using the Edirol R-09HR 24bit 96kHz Wave/MP3 Recorder for some time now and I use it personally too for making audio recordings.
The reasons are:
Records natively to mp3 so need to convert any recordings.
Can record to WAV, useful for those times you want an uncompressed recording for editing and later compression.
The microphones have been calibrated therefore are excellent.
You can use external microphones with them.
They record to SD Cards. This means that once a student (or member of staff) has made their recording, they can remove their SD Card and pass the Edirol onto the next user. This does mean you don’t need as many for field recordings. It also means you don’t need a computer handy to “take” the recordings off- having said that it does have a standard mini-usb connection if needed.
They run on AA batteries for what seems like forever.
They will record one on one interviews and whole room conversations.
Yes, they do cost more than your average audio recorder, but they are in my opinion real value for money.