How safe is this wallet to use for storing a lot of coins ?
Glad you like it.
In terms of security - if you set a password (when it asks you at start) it is fully encrypted with that password on the device, backups are also encrypted with a password.
So in this sense it is 100% safe - if someone gains access to the files on your phone this won't give them access to your money without the password.
That said phones are more vulnerable than regular computers, especially if rooted, and under the right circumstances your password could get stolen if the phone is compromised by the right app, so not 100% safe - desktop wallet remains the safer choice for really large sums of money, while phones are great for day to day spending.
Of course if you keep your phone relatively well secured, and don't store lots of dodgy malicious apps, then the above shouldn't happen.
The other weak point is your recovery phrase, if you copy this to the clipboard and it gets compromised then this could also be a source of attack, so if you plan to handle significant funds don't copy it to the clipboard but rather write it down manually.
The above advice aside, it is pretty secure, but common sense etc. applies.
Transactions within a blinck of a second, just tested it 
But ok, I get it. GL
