That works very well for me and the PHs I have walked with. Why it works is as follows:
(1) With the bolt handle skyward, the PH can see [even from distance] that the firing spring is uncompressed and can be sure of safety
(2) My experience is that the bolt is seating snug when pushed forward with handlle skyward. I.e. the chambered round mated to bolt extractor claw prevents bolt rearward movement without some force
(3) I carry my rifles muzzle down in a Z sling, so gravity is always working with the bolt to stay located [the bolt handle skyward solution may not work for muzzle-up sling arrangements]