UPVC beads are miles and miles and miles and miles better than steel.
just butter up the corners stick on the bead, plumb it, ....use a half inch two coat bead, lay over the web with yor scratch coat and you have the arris edge of the two coat to work to, no nails no hassle, no expense, no brainer.
S. Steel beads, havent seen one used in Years. I was actually given a box of them last year for the same price as a box of galvanised, thought I would save a few quid...ended up dumping them they are useless in comparison. Now you do have the opinion of a professional.