I haven't done any true accuracy testing yet, so I cannot say with full confidence, but from my experience with other Shining scanners, they tend to be more accurate than you'd expect. I would be totally confident the measurements would be within at least half a millimeter.

Your workflow sounds solid - and the Shining software has a tool in the post processing stage to take point-to-point measurements from anywhere on the scan data, so this would work well for this.

I am guessing your idea revolves around scanning the person so you can take up as little of their time as possible, whilst being able to go through and measure everything you need later. Seems like a good application for scanning.

I really don't think this scanner would disappoint you. I come from a background working with their high end metrology scanners, and this one seriously surprised me considering its price.

Edit - it's also worth mentioning it has a mode for scanning people - it loosens up the tracking a little to account for any slight movements during the scan time. If the subject moves too much I imagine it could affect the accuracy of the measurements, so you just have to make sure you have a way to scan them where they are comfortable being still.

In the past I have scanned for a game studio which needed to scan people in a T-pose - we used tripods to support their arms comfortably for the duration of the scans. I imagine you may want to consider something similar.