I purchased a Samsung Watch 3. All black and upgraded with a black finish metal band identical to the Casio. A nice setup. It has 4G LTE as well. The specs are great, but I ran into a problem. The small laser scanners used to get blood SP02 and pulse generated a 2nd degree burn on my skin inside of 3 weeks. Others with the same model had the same experience. Samsung was very secretive about dealing with customers with the problem. I sent my watch to their facility for "repair". They held it for 5 weeks trying to decide if a repair or refund was the approach. I had to lean hard on them to return my property as they really didn't want to do a refund. They feigned a repaired. On return, the watch performed as before. I only wear it for special occasions when I want a "dressy" watch. It can't live on my wrist without burning it. It turns out that even the Charge 4 puts a small 2nd degree burn on my wrist under the heart rate/SPO2 sensor window. It's just much smaller than the Watch 3 sensor "footprint", so the blister was smaller.
Solution:
Scotch tape over the sensor window. It is transparent and will block some of the energy from the laser but the sensor might still work without burning your wrist.............