I've had the SA 450 for 5-6 years now, really looked at this brand at first because I needed lightweight gear, but it sounded great and I was sold. It's getting real test now. When I bought it, I also bought a Bergantino 112 cab, but that limited me to 300W (which was MORE than enough when I originally bought it). It's now paired up with the Markbass 104HF so I get more air and the 500W at 4OHM (wasn't anything interesting around in a second 8ohm cab).
I think it sounds great, very 'pure' sounding for lack of a better word...I keep it mostly flat, but use the two filters - VLE and VPF for some coloring, but mostly the sansAmp bass driver does that work.