The M45 is the entry level deck of a series spanning through M-45, M65, M75, M85 (later upgraded to MkII and later renamed M88 to also support metal tape) and top of the range being the M95.
In terms of looks, the M45 lacks the detachable glass faceplate over the cassette door, the chromes toggle switches and thin and long transport switches. But it's a decent deck and plays cassettes well.
I have one, as well as an M65, M85, M88 and M95. The M75 appears to be rather rare. It's identical to the M85, only difference being it's FG-Servo rather than Quartz Lock.