Every iPhone investor I know uses the broker's app or Yahoo Finance. Both free, and for most people that is the whole decision. The real question is what you are tracking.
- Price is easy and nearly useless; every app shows it - Track allocation drift: did stocks creep from 80% to 88% after a good year? - Track hidden overlap: are two funds holding the same mega-caps? - Does the app aggregate across brokerages, or only see one account? A tracker that sees half your money is a rumor - Set drift thresholds and dividend reminders; kill the price noise
When an alert fires, compare before you act: Overlap ($4.99 one-time) lines up 108 ETFs, fees and overlap side by side.