I also wouldn't use Crashlytics due to a study that we've conducted in the last 3 months on 200 of the most used apps in Germany. We have collected real network traffic with a setup consisting of Wireshark and sslsplit (https://github.com/droe/sslsplit). We have discovered that Crashlytics will send GPS location data alongside bug reports. Probably it tries to collect as much data as possible.
These "free" analytics services have a dark side. The price for using them is that they get to build profiles of your users, with varying degrees of invasiveness. And once you sign up with them, you are selling out your users.
Given IP addresses, device identifiers, application identifiers, and timestamps - these 3rd party applications now have some pretty valuable signals that can be aggregated with other signals from other tracking methods to create a detailed profile linking users across devices, browsers, and geo locations.
All Customer Data is, or shall be, and shall remain the property of Customer. Customer Data shall not be used by Amplitude or its agents other than in connection with providing the Service or support under the terms of the applicable Order Form and this Agreement. Customer hereby grants Amplitude a non-exclusive, non-transferable, non-sublicensable, worldwide, royalty-free license to use, collect, transfer and process, the Customer Data for the sole purpose of Amplitude providing the Service and support to Customer under the terms of the applicable Order Form and this Agreement. In addition, Customer shall own all right, title and interest to the Results obtained by Customer through Customer’s use of the Service. For purposes of this Agreement, “Results” shall mean the data based on Customer Data resulting from Customer’s use of the Service.
We don't care who tapped button A instead of button B, we just want to know how many people tapped button A instead of button B.
Even if they don't use it that with ill intent themselves (there's really no way to know one way or the other), we can also be reasonably sure that it won't stay secure with them forever.