I know Blockfolio probably has good reputation but what about another less known app? What would happen if the phone is compromised or it has malware? What if the phone has malware?
If the phone is compromised it's your fault most of the times. I do think you should understand the fact that, these things are not to be taken lightly, you can download things from sources that you can't really be sure of and can download a malware with it very easily therefore you have to realize what you are doing and are the same time you are supposed to follow through with the security and everything.
Not just that, you gotta have some practical knowledge for sure. There are people who randomly spread their password around to people they know and get scammed as well, therefore it's not just about the site but it's more about you as well.