After upgrading to a new 16.49 Expanda from my old faithful 20 years old Swan, we heading off for its maiden voyage. My awning wasn't extended anyway when the storm hit, and we watched with horror as an awning on the van opposite flap around like Aunty Flo's undies and was torn off the van like crepe paper. I since seen two more awnings go west because of excess flapping. My baptism of fire has made me very paranoid
The deflapper will help to limit the flapping at the edges in lighter winds, but they won't stop the awning centre from banging up and down. The anti flap kit is a better option, but when used with a couple of curved awning roof rafters they are a great combination. We had the anti flap for the annex that we hadn't used for since we bought the van. We opted to use the deflappers for the convenience.
On one particular trip I put on the anti flap kit and curved roof rafters just to make sure it worked should we ever need to set up the annex ....... when I got home I threw the deflappers in the bin, and the anti flap kit and roof rafters are the only thing I use. I can usually still get it on after a few cold ones.