Earlier quoted context omitted.
No, there is no charge unless you start to put apps on the App Store. https://www.pcworld.com/article/2933052/apple-frees-casual-i...
The app will only run on your phone for 7 days[1] unless you pay Apple an annual fee, which is a non-starter if you want to write an app that you will actually use instead of merely test. No such restrictions on Android, Windows, or other platforms. Moto Sport 360[2] looks like it will fit OP's requirements. [1] http://mybyways.com/blog/new-limitations-imposed-on-free-app... [2] https://www.motorola.ca/products/moto-…
You're assuming OP doesn't want to pay for a developer account. They didn't say that.
Also, OP said they wanted to get data out of the device. The Health app has an export function. So no, you don't need to pay to do what OP wants.
I would take an Apple Watch + paid developer account any day of the week over Android Wear.