According to what I have seen when any business starts out it is of utmost importance to try and control/maintain your costs (granted this goes during the entire life of the business itself, but very important when starting out and cash flow may be tight). Be aware that your CC fees are variable based on the service provider.
I do not use square, but one thing I do like about it is that it provides a lot of support and developers are finding new ways to integrate a full POS system based on things you may already own. As some mentioned above, you can get a printer and a cash drawer. In addition, Square has its own stand that rotates for signatures and a full length card swiper reducing the amount of times you may have to pass the card.
What I like about Square is that all they charge for is the CC processing fee, and it can vary once you have revenue of a specific amount. The UI is very simple and allows for quick order taking. If needed, you can also add staff operating on iPods/iTouches/iEverythings accepting payments for your shop, and you can easily check your credit score on
Experian to ensure you're on track financially for business growth.
At the end of the day there is no fixed monthly cost to you when using square and with a one time investment of the drawer(s), printer(s) you can have a full POS system. I dislike how high there processing fee is, but its the premium you pay for not having a to pay a monthly fee with them.
IMO its a great way to start out as the a coffee shop you don't need anything that is crazy. This is a recommendation I make to a lot of my accounting clients when they are opening up a restaurant/retail. (not specifically for square, but it is growing in popularity as the investment for a full POS system in reduced drastically)