I've made quite a few button down shirts over the years, and Cashmerette's patterns (both this one and Vernon) are hands down my favorite — even with no adjustments, my first Harrison fit better than anything I've previously made or found in a shop. I have to make more, because I can no longer stand all the gaping buttons and bunching underarms on the shirts still lingering in my closet.
I did find I needed to raise the armscye quite a bit — this is a very common pattern adjustment for me and I'm surprised not to find it among any of the adjustment tutorials on this wonderful site. If anyone out there has the "arms can't move" problem where the sleeve is pulling at the biceps when the arms are raised, this is usually the adjustment that needs to happen. I made a second shirt with this adjustment and it fits much better. It was a bit awkward to do with the three front pieces, but absolutely worth it. I also found the neckline is cut oddly high in the front, but not enough that I've bothered to alter anything.
Between this one and Vernon, I think I slightly prefer Vernon, especially if you want to do anything that would want pattern matching. Vernon is also better for French seams, which I prefer, versus Harrison's princess seams really want to be either flat felled or overlocked. But this is still an excellent shirt. If you're a C cup or above, this is eons better than any of the big name patterns out there.