I'm saving up for a set of twin 12's. I've borrowed a set often enough to know I want one. Bit of weight to moving them around on the dry but they balance really nicely in the water. Now I know twin 12's are the norm, but I've also heard that twin 7's are good to dive. Last time the weather was kind one of the other divers was an Italian girl diving twin 7's. She came back with more gas than I did. She (sorry, didn't get her name) was GUE so was appreciably better than I was in the water. I was surprised to see a Gooist diving anything other than twin 12's, but she obviously didn't need the gas, the only difference in equipment was the size of the cylinders, and there was a swell running which made getting back into the boat a little interesting. My point is if you taylor your rig to suit the diving you do, then twin 7's are an option. Bigger than a 12, smaller than a 15, nicely balanced with some redundancy. Are the benefits of the twin 7's worth the added complexity and expense over a single? Are they too small to be considered a practical choice?