I'm starting to think there is a real difference between vehicles and body thickness.
I've never had an issue using the chassis punch on a vehicle. That's usually been pickups/SUV's and a few American cars.
If you had to buy one tool to do NMO installs, the purpose built NMO hole saws are the way to go. Depth limitation is handy, and they are designed for that. High tooth count on the blade means less chance of boogering up the body. Shorter pilot drill depth means no holes where you don't want them. It's a tool designed for a specific job, and it does it well.
Since I do this frequently, I have a few options.
Favorite is the Laird NMO hole saws. They consistently work. Drawback is the price. It's a bit hard for hobbyists to justify blowing $50 on a hole saw for one or two NMO installs. It does a nice job, but the price will turn some off. Replaceable saw blades mean it can last a lifetime (unless you loan it to someone and never get it back….)
The chassis punches are nice. They don't make as much of a mess and are a bit more controlled. Not cheap for a good one. You still have to drill a pilot hole. It has its place in my tool box. Not the most frequently used tool, but it is an option. It's a great option if you need to "imbiggen" an existing hole. They make a super clean hole.
I did get in a jam once and needed a hole saw but didn't have the Laird on hand. I went to a Home Depot and found they had perfectly useable 3/4 hole saws. Made by DeWalt and designed specifically for metal use.
3/4" (19mm) IMPACT READY® Hole Saw | DEWALT
No depth limitation, so not my first choice. It did what I needed and kept me from having to stop the job. It's still in my work truck, but next to the Laird hole saw now.
Right tool for the job, but there are options and choosing the right one depends on the exact application. For most people, the Laird hole saws are your best choice. Less chance of screwing things up. If it's worth doing, it's worth doing right.
Chassis punches are an option and a good choice for some installations. Not for everyone, though.
Hole saws designed for wood are not a good choice. The low tooth count/aggressive nature makes them prone to mistakes. No way I'd do that, but in my younger years I did. Glad I learned before really making a mess.
It usually comes down to the user, not the tool. Some people shouldn't touch tools. There's skill/experienced involved. User needs to be smarter than the tool, and that is not always possible for some.
Whatever, as long as it makes a clean 0.750" hole, you're probably OK. Just depends on the risk you are willing to take.
I still think my retirement side hustle is going to be roaming the country doing NMO installs for people that don't want to risk doing it themselves. I'll charge extra to do it late at night when your wife isn't paying attention. Might be willing to work for beer.
