3. Updates constantly breaking things. To be fair, this is also improving
4. There may still be instances where you have to drop into native code or split code based on platform. This means you sometimes will need to know: c#, xamarin.forms oddities, java\android stuff AND objective c\iOS. This may not be an issue for simple apps
5. UI builder is limited. The apps will be native looking but you won't be winning any design awards. Some things also seem impossible so it helps if the customer\designer\stakeholder is really flexible. If someone asks for an app to collect and display data, you will probably be ok. If they give you pixel dimensions and other minutiae run.
Also note that my experience with this is building an extremely simple business-y app for internal users.
1. Its moving fast so documentation is lacking and the "right" way to do something, posted 6 months ago, is wrong\deprecated\wonky
2. The tooling leaves a lot to be desired. Although this has greatly improved, there are still tons of steps to publish (https://developer.xamarin.com/guides/android/deployment,_tes...).
3. Updates constantly breaking things. To be fair, this is also improving
4. There may still be instances where you have to drop into native code or split code based on platform. This means you sometimes will need to know: c#, xamarin.forms oddities, java\android stuff AND objective c\iOS. This may not be an issue for simple apps
5. UI builder is limited. The apps will be native looking but you won't be winning any design awards. Some things also seem impossible so it helps if the customer\designer\stakeholder is really flexible. If someone asks for an app to collect and display data, you will probably be ok. If they give you pixel dimensions and other minutiae run.