I was given a couple, but I've also had one for over 10 years and that's a long time, so a backup wasn't a bad idea. I also carry one in my purse, one with my computer when I travel and one in my checked baggage. That way I always have one when I need one. I use them daily to check my O2 levels.
I prefer a Nonin Go2 Achieve. They are more expensive, but I've owned four or five of them and they have consistently been accurate and lasted forever. They are medically calibrated and respond quicker to changes than any of the cheap models I've seen. This is important, especially if you're someone whose O2 sats drop when you start to move. You know pretty quickly just how low you've gone.
One that reads the highest. It doesn’t improve your health but it does lift your spirits