JMR mfg used to make a very durable hole saw specifically for tube notching. They are trying to get them back into production. Right now they are unavailable. Shear notchers are fast but it gets hard to do high angle or weird offset cuts ( and it seems that most notches for roll cages are high angle and weird).
We use Wurth and Matco hole saws in our notchers. The rigidity/quality of your notcher and the way use it have the most effect on hole saw life. The notchers with shitty bushings and thin shafts (anything under 1") will EAT hole saws.. The good ones with 1 1/4" shafts, needle or other quality bearings will allow the saws to last longer.
Movement of the tube is a saw killer, make sure the tube is clamped very well so it cannot rotate or slip.
Use cutting lube and very slow saw speeds.. Most every drill is too fast, you need to gear them down or use a drill press.
If we don't make a mistake (loose clamp, etc) we can get 3-5 cages out of a saw...
Gosh, my business card says 'Tech Tyrant'