Stainless;
I used a HF tube notcher to build my roll cage. It worked just fine but it needed to be shimmed a bit to get the axes aligned properly. The key to success is to use a good quality hole saw and a slow speed drill. I found the hole saws from Dewalt, Milwaukee, etc are good while the HF ones are trash. A good cutting oil is, of course, a necessary thing. Getting a drill with a slow enough speed is necessary, too. A 1/2" variable-speed drill will work; I have a two-speed 1/2" pneumatic drill that worked very well. I used a speed of about 200 rpm to cut the tubes.
Regards, Neil Tucson, AZ