Pick One Platform, Build The App, And Learn*
Whichever platform you chose for your mobile app, choose only one. There will be mistakes but it's important for the mistake to only be made once, and if possible, only in one place.
As a mobile product manager you must be willing and open to being wrong. There will be problems. It is how you learn from the mistakes and make sure they don't happen again that matter. This is why picking a single platform to build an app is the most efficient use of time. On one platform you can focus your resources, quickly gather feedback, make changes, and roll out a new version quicker than on two platforms.
When time and money are issues you don't want to have to fix the same problem twice on two different platforms.
*This concept mainly applies to companies who do not have the resources to undergo app development on multiple platforms at the same time. If you have the time, money, and resources and find value in building for both platforms then do so at the same time.