So basically 2 400W rms subs, FLI are kind of a budget range, not great but ok for a first time round installer. But if what they are going in is anything like the size of that Corsa you were looking at then it will be complete overkill, 1 sub will be more than enough for such a size car. When it comes to Audio, especially subs, it's not how many you can cram in that counts as 1 decent 10" sub will sound infinitely better than 2 cheap 10" subs.