Comment by LifeUtilityApps

I built a similar tool to what OP shared, mainly for debts instead of investments, and I completely agree with you. My app only uses iCloud to sync and it keeps all sensitive data on the user's phone. Another benefit I want to share about this approach is it means that apps built local-only will never have the risk of one day going offline and being inaccessible due to the company closing down or turning off the server.