None of my business, but what do you have on your tablet that you are concerned about? Could you store it somewhere else? Or use software to encrypt it?
I am in IT security, I suspect if I wanted to, with a bit of profiling, I could find you on-line and gain access to your system. Will I? No, firstly and foremostly, I just don't roll that way. But if I were a bad actor, I would first have to ask myself if the reward outweighed the risk. Breaking in to individual devices is time consuming, easy to trace and 99.999% of the time, what you find is of little value. In my case, some pictures, a few very uninteresting emails, some phone numbers and email addresses.
Much better would be to put malware on your device and capture keystrokes, have those sent to some compromised server, discard everything that is not interesting (look for 16 digit numbers starting with a 4 might be VERY interesting). Then come back every few days and pick up the interesting data. Much harder to trace and a much higher yield. With our Android devices, getting malware installed is very difficult (OK, actually easy) but easier to avoid. Don't sideload. Very few (if any) malware is installed via the play store. Your windows computer on the other hand, can get malware daily, most is harmless, just tracking for targeted adds, but some will be keyloggers.
The other high ticket is phishing. Send you an email asking you to log in and change your password (make it look like it came from your bank). Many people are so concerned they will click the link, and expose their user id and password to the bad actor. You send out a million emails, if 1% respond, you could get hundreds of thousands or millions easily. The thing that gets me, if you get an email and it concerns you, why click the link, you likely have bookmarked your banks website, just go directly and change your password (then the bad actor is not part of the transaction and you are safe).
While it's possible a bad actor (or bad government) may want access to your device, but if the data on it is of little value, and if you are generally operating within the laws of your government, you are just not a target.
Personally, I think the picture issue you had, is not related to the chat app, and the app you have is likely not an issue. I would be more concerned with the content of the chat (is there anything there that makes you a target, or causes law enforcement concern) than with the actual app itself. Lastly, look at the number of installs. If an app has been installed 50,000 times (or more) and there are not a bunch of reviews saying it's spyware, then likely the developer is a good guy providing a valuable and useful tool.
Just my 2 cents worth.