How much power do I need to soft solder small piping?
The tool you are looking at is a soldering iron.( not a torch ) Most are powered by electricity but some, like the one you mention, are powered by butane gas. 

For sweating copper pipes that tool will not be sufficient or provide enough heat. ( it will melt the solder but it will not heat the pipe up enough to make a bond with the solder. ) 

You need a Mapp gas torch

There are Flame-less options, i have never used one. 

Here is brief synopsis of soldering. Family handyman. 

And a YouTube video.