Compared to online processing giant Paypal, Revolution Money Exchange is a baby, only a couple of years into handling the transfer of funds via the internet. Though it appeals to individuals, some small businesses have begun using it as well. It does promise low fees and from my limited experience, it was very user-friendly. There also aren't any monthly statement fees or contracts - you aren't locked into several years and forced to pay an early termination fee if you stop processing or change providers.
That said, there are many reasons why businesses might choose a more secure merchant bank. Though RME offers some perks as I mentioned above, it is entirely possible to find a credit card processor that will forgo the early termination fee and bill no monthly fees as well. These things can be negotiated when you sign up for an account, especially with the best merchant companies. Those companies know that their rates are excellent and a better deal would be hard to find, so they don't feel compelled to lock you into anything by contract.
I would recommend checking out the Revolution if you want to start accepting payments quickly. Once you're set up, you can shop around for a better merchant account.