My Wahoo Bolt is dead accurate and does not use a lot of power. It never falls off the bars and starts immediately when I start a ride. It also swaps seamlessly between bikes and when on the trainer, all automatically detected. If there's a wheel sensor it sees it, if there's a cadence sensor it sees it. It displays my power meter. It records all data accordingly. All data gets stored offline in multiple places so it is never lost. There are more display modes than I can even count and so many stats that I can't keep up with it all, but you pick what you want to focus on.
I just don't understand why people say they are not accurate or are unreliable. I tried using a phone for a while but it always ran out of power on a long ride, and only recently did I use it with a separate battery which did make a difference.
But yes, they are a bit expensive.