I have the M50! And I'm VERY satisfied with it, it is probably the most price-worthy Workstation currently on the market, since it can do almost everything that the high-end flagship keyboards can do but at about half the cost.
However, I have to admit that the Piano sounds are not very good, but as the M50 is quite easy to understand and use, you can make them sound good if you learn how to handle the parameters. And considering you're going for a 61 key version, I guess you don't intend on playing primarily piano sounds on it anyway.
So, if you're interested in buying the M50 (I guess you've done some research to see if it fits your needs?), I would definitely say Go for it!