One of the nicer features on the MZ-R55 is the Digital Syncro Record. When connected via a digital (optilink) cable, the MD recorder allows you to automatically start recording when the sound source begins playing. The digital input also allows for automatic track marking at the same place as the original source (assuming the original source is digital as well). This makes life easier when recording tracks from albums such as Pink Floyd's Dark Side of the Moon, where the standard two-second gap between tracks does not always exist. The analog input, however, still relies on this two-second gap, though this isn't much of a problem since you can move the position of the track mark around at your own whim.
In addition to the combined digital/analog input, the MZ-R55 also sports a microphone in and a line out. Those college students out there who like to tape their lectures will find this MD recorder a suitable replacement for your old cassette recorder. However, you'll need to get the microphone separately as one is not included. The line out is the same as the line out feature available on just about every portable audio device on the market. It would have been nice to include a digital out on the MD, though it's not a feature most MD players have anyway.
Of course, one of the most important aspects of any portable audio device is how it sounds. Using ATRAC4 (the MZ-R55s compression technique), the MZ-R55 delivers fantastic quality audio that is nearly indistinguishable from the original CD. In addition, the ear buds provided with the MZ-R55 deliver adequate bass (for ear buds), especially when you turn on the Digital Mega Bass® amplifier. Thankfully, the ear buds are of average size and should fit comfortably in your ears.
Though rather feature complete, the MZ-R55 is not quite perfect. Its biggest drawback is its battery life. The included rechargeable battery provides (on average) a mere 2.5 hours record time and 4 hours playback. This makes the external battery adapter a must. With the additional power of two AA batteries, playback time is increased to a comfortable 9.5 hours and record time to 14.5 hours. In general, you'll probably have the AC power adapter plugged in when recording, as wasting precious battery-life while not on the road lends itself to more frequent trips to Costco. Unfortunately, the MZ-R55 cannot recharge its battery while recording, so some of you may want to buy batteries (and patience) by the bulk anyway.
One of the great advantages of the MD format over its predecessor the audiocassette is the ability to title your tracks and albums. However, titling can be a tad time consuming on this unit as not only are the buttons on the base unit small, but there is no jog dial to easily select characters. While each title can be up to 500 characters long, you may find that any title over 10 characters to be rather tedious to enter.