soldering guns generate heat by resistance.. high current is passed through the tip and heats up.. when you let go of the trigger it cools.. those are like 100w... you can still get burned when the trigger is off.. also they are heavy.. no one uses them anymore..
people still use soldering guns, for like large connections, automotive wiring, heavy duity high power equipltment ect. but for sure not for electronics.
I use a 100/140 watt gun. I prefer it to a 30 watt one I bought at radio shack. its nice to not have to wait for an hour before you can use the gun. If I have to make a quick fix to something I can pull it out plug it in and make the solder in less than a minute.