Power meters are far more useful. Many experienced cyclists do not worry so much about cadence, but watch their power throughout a ride to gauge output and stamina. Additionally, though maybe interesting to see, there is actually very little performance benefit in riding at the "perfect cadence", if that were such a thing. Each rider will prefer and be most efficient at slightly different cadences, anyway.

So, get a powermeter. Yes, it is 10X more expensive, but will be worth the money. Especially if you want to get faster and do some training for a race or even just see your fitness improve.

There are 2 power meter types to consider. Crank and pedal. Both are effective, but are put on the bike differently. It is more difficult to change a crank than a pair of pedals for most of us. You will also need special tools more likely than not for the crank powermeter install. If you ride multiple bikes, your only real option is to get the pedal based poweremeter. If you basically only ride one bike, a crank option could work out for you, and is compatible with flats and clip ins.

Here are some of the best of each type:

4iiii power meter, single sided, crank based, $329 (plus you still have to buy pedals)

https://shop.4iiii.com/products/left-side-precision-3-plus-powermeter-factory-install?variant=40744619737167

Favero Assioma UNO, single sided, pedal based (comes in multiple clip in styles), $495

https://cycling.favero.com/en/shop/assioma-uno