That looks like a decent gun for a home user. When you start dropping in price the duty cycle decreases and the welder can get fairly warm if you do a series of continuous spots. It's not a bad idea to familiarize yourself with resistance welding before actually starting:
http://www.millerwelds.com/pdf/Resistance.pdf
I have an old spot welder here I'd love to try. It's a professionally made model similar to this one:
http://www.vintageprojects.com/metal...WeldingGun.pdf