Bought this sub to compliment a pair of Opera 12's that I also own.
The sound is great, and it works brilliantly with the 12's adding some great low end. However, in my opinion the sub always clips quite easily whereas there is a lot more headroom to push the Opera 12's more.
I know adding a second sub would alleviate this issue a bit, but felt this sub would give a little more power before it starts to clip.
Overall, great sound and perfect match with a pair of Opera 12's however if you need a lot of power you would definitely need to buy a pair of these. A single Sub618 won't be enough.