They clip on with 2 rubber straps with holes in, onto 2 clips on each arm. So 8 straps in total. I fitted them in about 5 minutes but they need a little tweaking in good light before I use them. They have standard adjusters similar to these.
In fact they they are very like these though they have 2 straps on each side and don't have the clip at the top of the mudguard.