220 minus age is stupid (for me).
I found out pretty damned quickly that 180 or 190 bpm were enough for me. I can climb any of the Cornish hills without going above that, and I found it interesting how my HR varied with respect to effort. Unless I was hitting 180bpm climbing a hill, I wasn't trying hard enough.
I found that using a HR monitor, I was riding harder trying to keep the HR high. This may be a Good Thing if that's what you want, but for me, it became a Pointless Thing, because I knew what figure I was going to see in the data field.
I no longer have one now - I sold it - and TBH, I'm enjoying my cycling more. I don't worry one iota about my HR. I don't obsess about it and can forget about it completely.
If you want one, that's fine, but my advice is to use it for a few months and get used to the figures it shows you. Try and see what numbers it gets up to when you go for it up a long hill. By having the experience with it, you will KNOW what you want from it.
Good luck.