Yes. Probably.
"A power meter allows riders who are serious about performance and training to monitor their workload, track progress, and pace efforts during important events or races." 1
If you are at the point in your cycling journey where you know what a power meter is and are considering whether you need one or not, the answer is yes. It is the most valuable thing–besides a bike computer–you can get for improving your bike training.
Will it magically make you a better cyclist? No. But it will allow you to do structured workouts and measure progress over time. I have heard it said repeatedly by many different people that you can train solely based on Rate of Perceived Exertion (RPE) and that athletes trained that way for decades. While that is somewhat true, I would never suggest training solely based off RPE to anyone, not even experienced cyclists. RPE is subjective and can be influenced by a number of factors unrelated to cycling. Power is objective and measurable externally from you. RPE is useful and worth tracking, but it is equivalent to saying a person is warm vs they are emitting electromagnetic radiation at 15 μm.
Which Power Meter Should I Get?
There are a number of power meter buying guides out there that you can find with a Google search (example). The three types of power meters I have personally tried are pedal, crank arm, and crank spider. My advice would be to get a crank arm one, if you can find one that works for your bike. They're one of the cheaper options, are as accurate as most cyclists need, and should last you a good long while.
If you cannot find a crank arm power meter, then power pedals are a perfectly acceptable backup option. Back during the COVID pandemic that is all I could find for my gravel bike and I still use them today. If you have never switched your pedals, then I would suggest going to your local bike shop and asking for a quick lesson. Once you do it a few times, it should be a super simple 5 minute project to switch between bikes, all you need is a pedal wrench and a small tube of grease. Do not be intimiated, you will get the hang of it in no time.
I have one bike that has a spider power meter and it is, with no exaggeration, amazing. Very accurate, measures both legs, and it zero-offsets automatically. Pretty much a worry free option. If they were not so darn expensive and a bit time consuming to change chainrings on, it would be my preferred option. If your bike happens to come with one, excellent, if not, I would likely only suggest this to cyclists who enjoy spending money.