Mmmm you’re talking about key resellers. A full retail version costs $150. Keys from key resellers are notoriously unreliable. It might work forever, or it might stop working a week after you authenticated. It’s more or less a gamble.
Great if it works for you, sucks if someone just wasted money (however little) on something that’ll stop working - especially if it’s grandma’s machine.
Also, hedge your bets a little better, buy the ones that cost $10 or even $15. Historically speaking those are a safer bet.