Agree w most of your comment except for last paragraph.
Cardia, given that it advertises in prime time is definitely a mass market device.
Your comparison of apple’s multi function watch with cardias single purpose device is inapt both as a Badis for apple abusing market and meaning people buying the Watch meaning people in generally poor health.
You say cardia is recommended by cardiologists, I have no quibble with that but it is also promoted to the general public. It’s this second mass market category that compares to the Watch. Both are an attempt to increase sales by democratizing ekg functionality and the best part of this is that many folks with undiagnosed arrhythmias will detect something and have the chance to see a doctor before a problem strikes.
Yes I agree they promote Kardia to the general public, I've seen them advertise on general television even, but it is still not something people are going to generally buy. Where as an ECG reader has been in every Apple Watch, I guess apart from the SE, since the series 4, and as a result Apple has sold millions and millions and millions of them. I don't think Alivecor will be anywhere near those sales figures. But I could be wrong.
But you would generally buy a Kardia if you need it, you don't buy an Apple Watch generally just for its ECG reader.
Agree they are useful for picking up early heart conditions, but I'd imagine overall it's a pretty small percentage of Apple Watch owners who have a condition? Well I'd hope so at least...