If you can find a Mizuno cart I'd highly recommend using that DNA analyzer to get your shaft recommendations. Gave me a list of options which I tried (very important). It recommended a PX 6.5 (which I absolutely hated) X100, and KBS Tour X (which I absolutely loved). Once I found the shaft I wanted it made the rest of my searching online for clubs much easier. Before that I never realized how important iron shaft brand differences could make versus the different swing profiles. It's literally 3 or 4 swings at a box store when you can find one and for my money it's really accurate.
The problem with an online fitting is I could plug in my swing speed, flight dynamics and transition characteristics to come up with a range of options, but the realities in hitting them was too far apart to really bring it down to an option that would make me happy. If I had bought a set of irons with PX 6.5's I would have thought they were garbage because every swing felt like I was swinging a piece of rebar.