Flex or three
If it's a microlight, it doesn't matter whether it's a flex wing or a three axis, if it's windy both can suffer the same fate.
Microlighters tend to keep a good eye on the limits, ours are considerably lower than the general GA limits. However experience can increase the "window" and microlighters can be found out in all sorts.
Depends what you want. Flex is great fun, but then so is three axis.
Personal choice at to what makes you smile, but I wouldn't say that one is cheaper, or safer.
However you can't beat looking straight over the side of your hull in a flex!