I have the bigger Firstgear Laguna tank bag and I love it. This is real quality stuff and Firstgear was sure to include A LOT of good features. The magnets are super strong. I am sure the smaller 'mini' is just as good. I don't think you'll be disappointed with it. I wrapped the quick-release clips around my front tree and I am telling you that this bag is mounted very securely in this fashion.
Also, I have the exact same matching Laguna trunk bag from Firstgear that I used ONE TIME before getting a Shad hard case trunk. PM me if you would like it for a 'very reasonable' price.