I already own 2 Hi Viz mesh fasten-up-the-front vest objects*; one is an official Audax UK one from several years ago (possibly bought but not used for a previous PBP), and one I got from Lidl last year for a couple of quid for running in. It's a bit lighter and packs down to about 1/3 the size of the AUK one.
I'd assumed they weren't EN471-compliant but I just checked and they both are labelled as such, and are CE-marked accordingly.
*MV cunningly avoids admitting ownership of anything beginning with g