I added a gopro fairing using velcro. Check flight showed no indication of becoming loose. Upon first review there is less wobble in the camera because of vortex shedding. It should have less drag. patent pending.... by Mr. Duct Tape and Captain Velcro
Do you notice you need more rudder to yaw? You're adding more vertical surface aft of the CG so you should be getting an increase in yaw stability.
Great that it reduced the wobble, now you need to put a small flap on it and add in one of those active servos from the RC world and you have active stabilization.
I didn't notice any handling difference. direct xwind 10 G20 and bumpy, so not a good day to notice any fine handling differences. it's not rigid. I could disconnect the fairing at the velcro by hand with less than a pound of force if I pushed at the trailing edge. the good news, it didn't fall off.
Low aspect ratio decreases the lift-curve slope, so there's minimal side force developing with sideslip angle. In other words, it's not effective as a fin.
The Granville Bros (Gee Bee fame) found that a 3-1 ratio of length to width had the least drag vs sfc area. Beech or Boeing found the same thing with engine cowlings. So, your fairing is quite a bit longer than required.