Alan, after experimenting with both the Piano 36 and the Pro 36, I think you can bank on there being some work involved in getting them up to scratch, unless you are buying that rare example of a new old stock item. That said, I believe you can get them going very well, with a bit of patience and work. Once repaired up to a standard where the bugs have been ironed out I think they are as reliable as any other melodica.
I am not budgeted for putting a lot of money into repairs and baulked at paying for the broken reed to be replaced on my Pro but I consider that the $100 Australian I spent was well worth it, on an initial investment of under $100 for a good example apart from the broken reed and some general tuning and minor maintenance problems. Maybe I have been lucky in that the Piano 36 and the Pro 36 I bought sight unseen off ebay were in more or less good condition and not too badly treated.
It would appear that performing musicians favour the Piano 36 and I can understand why as it is a great instrument, of course reliability should be a first concern for the professional musician.
The M-36 I am getting is the black version as pictured in the review write up section on this forum. Looks pretty much exactly the same….