I'm 150-155lbs, 5'6, it works fine for me. A bit heavy but it does not carry too well if you place the back band on your head. Thigh braces did into my skinny back. That aside it's a good boat.
I used to paddle a M Burn. The Mystic feels a little more forgiving than the burn, especially on turbulent eddy-lines. It is also a smidge wider than a burn, will feel a bit sluggish if you are used to paddling a burn or something with that much edge. But is by no means an unresponsive boat.