Good idea, needs to be taken a bit farther
I love the idea, but I think it could be improved a few ways:
1) The measurements are all around the crown of your head. Therefore their recommendations may be completely wrong for the height of your head, or shape of your jaw/cheeks or neck. In my case, the first helmet that I tried (recommended by the report) was very loose on my cheeks, which is dangerous.
2) Even the crown of that helmet was too tight, so there may be some disconnect between the measurements submitted and the report result.
3) I'd love to see 2 items added to the report: how many shell sizes a given helmet model has (e.g. cheaper models tend towards a single shell size, while higher-end tend towards 3 or 4); the safety rating of each helmet (DOT, ECE, SNELL, SHARP).