Im not an expert but I don’t think the ecg improves as the models and chips do. If budget is no issue buy the watch you want. If you want to keep price down the 7 or 8 have good sales and will do what you need. I just purchased a stainless steel 7 about 6 months ago on sale and would rather that than an aluminum 9 series. PS I have been using the ecg on mine as per cardiologists recommendation for 3 years now starting with the 6 series.
This is my biggest gripe. I love everything about the watch, setting my sleep schedule and tracking sleep. But if the haptic alarm goes off it either scares me out of my sleep cycle or I snooze until I’m late. The sleep schedule wake up alarm is perfect for me.
As far as i know you can’t have nighttime focus, with tracking and phone alarm.