I've always used a chest-based heart rate sensor until I started trying wrist-based about 4-5 years ago. I've used countless brands and models (ranging in price from about $49.99 up to about $399) on my wrist - and literally none are as accurate as the chest-based strap. The chest strap responds immediately to increases and decreases in heart rate. Whereas the wrist sensors always seem to lag, sometimes by up to a minute or so.
The wrist-based sensors always seem to differ depending on where on the wrist they are worn - high, low, inside of the wrist, outside of the wrist, etc - by maybe 5 bpm or so.
In either event, if you really want to test the accuracy of the wrist-based sensor, you should really compare it to the output of a chest-based strap.
In fact, the results will largely be personal - because the electric signals may differ per person greatly in different areas of the arm.
Needless to say, my apple watch is worn daily, but when riding, I have gone back to a chest-based strap.
That all being said, there is a guy that reviews these gadgets and will often wear 2-4 sensors while working out, and post an overlay of the results from his workouts. The baseline should generally always assume that the chest-based straps are accurate. His site is called DCRainmaker, if anyone wanted to look up his comparisons/reviews.