Just let me stop you right there as I reiterate what Apple App Store has to say about HalloApp and its privacy:
Data Linked to You
The following data, which may be collected and linked to your identity, may be used for the following purposes:
* Contact Info
Phone number (your most prized privacy info). This is a FULL-STOP right there in these days and ages.
* Contacts
Contacts (your entire address book, who would want to pull down the proverbial pants and leave their derrière exposed and tangle with the wind?)
* Identifiers
User ID (probably your Apple ID, after sufficient reverse mapping).
* Diagnostic
Crash data, not hard to get even more relational mapping from this.
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# Signal
Compare that to SignalApp:
* Contact Info
That is entire optional and can be left blank within the Settings->Contacts->My Card of which that should always be blank.
Nothing to see there, move along.