I am not convinced the master test kit is ever a must. If you enjoy working with the chemistry, it's fun. Maybe if you have a stubborn and impulsive, impatient personality, the test kit results can prove what people tell you. I'll grant that.
It remains that about midway through my hobby experience, I crashed one tank by overstocking. I don't think a test kit would have helped. My eyes were bigger than that tank, and I impulse bought. I've set up hundreds of tanks, and even as a kid and as a teenager, never had another ammonia crash. I have no special insights now I didn't have when I started as a kid, beyond the need for water changes as they were not suggested way back then. I followed simple rules - stock lightly, and always with the full size of the fish as a baseline. Feed carefully, and with experience and changing research, change water with regularity (30% weekly without fail). These happen to be things you have to do with a test kit anyway.
But if you are patient and organized at all, you don't need a test kit. Don't overstock, grow things and do your chores... I'll wager most people who buy kits use them only when the tank looks like the day after a riot. People who test methodically probably take care of their fish methodically. But it's a debate.
But if you say that even a newbie doesn't require a test kit, what are they to do when they go onto an online forum with their usual newbie problem questions?
The first answer to such questions from the guys who are trying to help is usually, "what are your parameters!"
Without said test kit the newbie hasn't a chance of answering this important question and so the guys who are trying to help are just poking around in the dark at best.
A test kit is always handy to have, more so for the newbie, less so for experienced hobbyists.