Yeah SBI Buddy app is very safe since you have to enter your PIN during login, Sending Money, Transferring Money, Recharge & Bill Pay. Even when you add your money the combination of PIN and your OTP makes it tough for anybody to misuse it.
In future, I think apart from PIN an OTP feature will also be introduced when the limit of Buddy increases from 5000.
So don’t worry, treat the SBI Buddy app just like an ATM which also has a PIN.
You can avail additional security by locking the App by another PIN by using App Lock.