Sonic Tronic pumps are great. You MUST mount them as per the instructions. I have had 3 now. I just replaced one and found out it was my wiring, not the pump. My first Mark X lasted about 8 or 9 years. I think that is normal for a sonic tronic mark X. And they ship fast to. I think McDaniels RC is the distributor. Search.
I had a Six Shooter years ago. It worked great for about a year or two. Then the tube inside flattened out and the pump had almost no volume to speak of. It took a long time to fuel a plane. Hanger 9 has a good little hand cranker. ( Just don't loan it out, you will never see it again.) It WAS my "back up" pump.
Sonic Tronic Mark X comes in a 12 volt and a 6 Volt version. I don't believe it is a good idea to run 12 volts through the 6 volt motor.
I like the Sonic Tronic because it is the most compact and I feel, the most reliable electric pump. They are fast and clean also. They generally don't die all at once. Toward the end of their life, they get slower and louder. But they hang in there for some time before they quit completely.