It fits and I would say it's true to size (what ever that is, it's a shame that they doesn't write the measurements on the garment).
My estimate is that OS fits a size XS to M.
The OS size (cheast) is in CM
85cm total length
80cm to last whole
68cm to first hole
The OS size (cheast) is in INCH
33.46 inches total length
31.5 inches to last whole
26.8 inches to first hole