Suspicious as of how? It only checks the balances of the address, you don't need private keys at all.

You can check your friends address or any other address in particular doesnt have to be yours.

It's basically a tool to quickly check multiple addresses balance, even I use it, but as I said earlier, just use if on a pc that has no bitcoin wallets on it, you will see that its perfectly ok.

I can sell you the source code if you want for 0.02 BTC to test it yourself?