i have a 25 watt, that i got for 9$ it works very nice, i built a pedal with it and i ordered 1 meg pots to go in both my guitars and i plan to use it to do all the soldering work.
My only complaint , and it is sort of a biggy is that it doesn't have an on off switch, you plug it in it's on . So if i were you i'd make sure to get one with an on off switch, and try to stay to a lower voltage , too high get a little too hot and you'll fry the pots on your guitar.
i was talking to the guy that was helping me out with getting a voltage meter and i metioned i need a tip for my soldering iron and he said that the cold heat soldering iron is the best. Yeah the one on TV , he said he worked on computers and got one and said he doesn't use his old one any more . He said it worked well and he said it would be perfect for what i was doing . I dont know i didn't get it but you may ask one of the guys there what they think about it.