Have not yet used coinomi wallet as it is not open source. Isn't it a multi crypto wallet? I personally don't preferro usesuch wallet, I use the official wallet of coin to hold them. It may be secure but imagine you have lost access to the wallet or someone else have access to your coinomi wallet. You will be left nothing.
Yes, it is a muti-coin wallet and there are too many supported altcoins on this wallet. Despite being a closed-source wallet, it's still popular and there are still users who keep on using them.
I guess being aware of the wallet we're using is very important. It's still best to use a wallet that you trust and you're aware of the security issues or how strong the security of that wallet is.