If these are the same tanks produced by Turbine Cubs of Wyoming (now Backcountry http://www.supercub.com/) my Cub has them. I've seen no issues with them.
The BBI tanks are made by Nick Smith. They are a bit heavy, but otherwise a good tank. They strap in securely around the spar, like the stock tank. There is a compression tube that goes through the tank. Don't see how it could come flying out in an accident or other accident any more that any other tank.
The ones I have worked on were held in with an aluminum stap instead of steel like the Piper tanks. In an accident the non-extruded piano hinge that holds the straps together streches out and the tank comes out. The ones Nick provided Greg were different and way heavy, they clamped around the spar.