The Response amps are certainly excellent value for money in the bang-for-buck stakes. I ran 2 4x100 amps in my previous car (a Corolla hatch). Never had any problems with them. Entered my car in an SPL comp using 2 Jaycar Venom 12" subs in a 4th order bandpass box running off 1 of these amps (bridged 2 ch each) and got a reading of 143.5 dB. However this was with an upgraded battery, and some heavy-duty cables.
Quality-wise, the Jaycar speakers ain't too shabby, but there are many better brands. You can't go past the amps though, they are pretty much indestructible if set up correctly. The thing I like about them is that on the box they quote power figures in RMS, rather than the airy-fairy claims of certain other brands that quote MAX power.
Paul