I'd agree no system is secure, and with enough money or determination then anything can be cracked. However, you're advocating an android based mobile, which are highly susceptible to attacks, malware, hijacking etc etc.
Anything UNIX based is proving to be much harder to crack. Im not aware of any real malware for the iOS, no reports of people being infected by viruses or trojans. Yet there is plenty of evidence to show that this has been done on android based operating systems.
So, my point is that stating to get a proper phone isn't helpful or accurate. Unless you're telling the OP to get a nokia from the 90s? In which case, yes that would be super secure as its not a smart phone.
I think most of those app stores got shutdown. TBH the whole jailbreaking community around the apple devices has gone pretty quiet. With the way things are going forward now, i'd say security is more important than some free games/apps. I even buy my xbox games these days