Very few PA cabs are especially suitable for bass rigs, and not just cheapies like those! PA cabs usually aren't even designed for lows since subwoofers are used for to perform that duty in PAs.
+1, PA systems normally are designed to work with a sub and normally w/ a crossover. If you have a good system though, it can be very flat and neutral. A couple bass cabs can make good PA cabs though, at least compared to guitar cabs.
