Someone asked my opinion on my new one in another thread, here was my reply. If there are any specific questions, I would be happy to try and answer them. As for efficiency, I do not know how to determine that exactly? I will say one thing though that I failed to mention in the reply below, I asked on here about fusing and was told to use a 200A fuse, however, the instruction manual says to use a 300A fuse.
"I love the Crunch amp so far; I have only had it up and running for about 3 days. It seems to have a ton of power, however, I am not even sure how to tell the efficiency. FWIW, I have a stock battery (65 series, which is close to a 27) in the front, stock 160A alternator, and a BatCap 800 in the back. I have the Big 3 and pos and neg 1/0 runs front to back. With all that and running 50 mph down the road, the lights still dim pretty bad. I guess I need to upgrade the alternator, yet I can not find anyone who makes one for my car, and/or add some more battery(s). But overall, I have been very happy with the Crunch amp thus far.
Any tips on how to measure its' efficiency would be great..."