Either method appears to be popular - so long as it's done right. Plenty of threads on here regarding removal of powder-coat from wing stays, using big-heads&cable ties, or wrapping Sikaflex around the stays.
Me - I've bolted them on, but wish I hadn't. Now have cracked wings around the bolt holes. ☹️
On the bright side - they'd have cracked anyway from stone chips
Richy