Just noticed this.
I used re-useable cable ties to secure my 'bar-bag'. They definitely work, but they don't look especially pretty. Basically, the bar-bag is on my winter commuter, and I use it to keep my rain cape in. It never comes off, and I don't really care what it looks like.
I bought a box of re-useable cable ties, so happy to send you a few gratis if you want to try them out.