These devices are good stuff.
Exercise is crucial. It could save your life, not just by all its benefits, but, also for allowing you to catch heart disease early.
Note that the device monitors sinus rhythm. It won't tell you if you have a blockage in the same way that exercise will.
You can give yourself a stress test at any gym, or a doctor will happily charge you a bunch of money to do so.
You should regard exercise as next to the gold standard for seeing problems in your heart. The gold standard is a cardiac cath with dye.