The fact that faces wouldn't be 100% compatible with Tizen is definitely a valid concern, and we're working on ways to address that.
The upside of using Android Wear 2.0 complications instead of the internal Facer tags are that the end user can swap your complication with whatever they want, including a ton of options we can't support on our side. One basic example would be your face including a weather complication by default, but the user being able to swap that with a complication showing the stock market instead.
The second upside, is that a lot of these complications are tappable and can launch 3rd party apps on the watch. In the previous stock market example, this could launch a stock market app on tap. This would be transparent to you on the designer side - the only thing you need to define is where the complication is, and what type of complication it is.
If that's interesting to you guys, we can prepare a collection dedicated to these faces and promote it heavily in the next few weeks.