Yeah, Mobile app builder extensions will surely fulfill all your requirements that you want for your app. I would suggest to go for Knowband's mobile app builder which provides a ready-made framework to develop a Magento application for your web store. Developed applications are both Android and iOS optimized and they do have numerous features which halves your work load and doubles your store revenue.
Yeah! You can opt for mobile app builder. It will surely provide all the features and functionalities in your mobile application. I would suggest you to go for Knowband's eCommerce mobile app builder. It is by far the most pocket-friendly and advanced mobile app maker extension. Knowband even provides 3 months support free of cost.
I would say mobile app application development is more difficult than native mobile application counterpart for the following reasons.
So I suggest you buy the Mobile app builder rather than hiring the Mobile app development agency.
It's good that you are moving with the trend and converting your website into app.
Le'me resolve your confusion first, If we look with respect to cost then app development agencies will be costly enough for app development with respect to app builder extensions.
It's not like they won't be able to fulfill your requirements as your apps will be developed the same way whereas app development agency will be for developing custom app.
So, I suggest you to go for app development extensions or either you go with MageNative.
They will be providing you with all your requirements at a better cost. They provide 30 days free trial for the apps. Apps support multi-languages as well as RTL along with unlimited push notifications and social login.
You can also follow this link- https://marketplace.magento.com/ced-magenative-mobile-app-for-ios-android.html
As per my experience, I would like to suggest you go for a Development agency as they will be working professionally and you may not suffer your project left over in between.
You may check this Company for App building Projects- MageNative Mobile App Builder
Recently I used MageMob App Builder. In this extension, many features are available like Push notification, themes, etc. In Application, you have a limitation of themes but in extension, if you want any more you can go with customization.