yes it is both easy and trustworthy.
it is a very convenient service for beginners to start with bitcoin. you can easily make a wallet with they which looks like everything else like Paypal or other online wallets. and you can easily deposit money and buy bitcoin and then hold it there to spend later.
but remember that it is not a good bitcoin wallet because you don't control the private keys. if you want, start with them, buy, learn how bitcoin works then get a real wallet, preferably a hardware wallet like Trezor.
Thanks for your reply, I bought a little bit of bitcoin, ethereum and litecoin on coinbase this week. Just to experiment, do you think eth. and litecoin. are good investments yourself?