I wouldn't agree with this part. I am skeptical with some of them. But it also depends on the platform. I have used Coinomi for Android for a long time and I have never had any issues.
There were some claims made against the Coinomi desktop client by one user here on the forum in the past but if I am not wrong that case is still unresolved. Last thing I read is that Coinomi is planning to sue him for making the findings public, and putting user funds in jeopardy, instead of reporting to Coinomi first.

Exchanges, even the best ones, have been hacked so many times. Binance, GateHub, Bithumb, Cryptopia... just to name a few of the most recent incidents.