With Scubapro BC's, you don't need a second BC tank band since the Scubapro BC Tank band is very secure and will be most difficult to open or have the tank drop. In addition, these two BC's have a tank valve strap that would help in retaining the tank should the main tank strap break (VERY unlikely event that has never happened to me or anyone I know in over 30 years of diving with SP BC's).
P.S. The SeaHawk 2 BC has 3 straps, the main Tank band, a Velcro narrower tank band and the Tank valve strap.
The SeaHawk was FAR easier to put on the tank and take it off using the SP cinch strap than a two tank band BC (cam bands). I don't want to deal with trying to attach a BC with two standard cam bands to a tank compared with one Scubapro BC tank strap.