The API is very cool, but the flat 2.9%+0.30 isn't so cool. Shop around before you use Stripe. Make sure you're comparing apples to apples. Many places will quote a "qualified rate", which isn't the same as a flat rate in any way. For comparison, Paypal Pro starts at 2.9%+0.30, like Stripe, but drops to 2.5%+0.30 at $3k/month, then 2.2%+0.30 at $10k/mo.
what difference does the rate make, if they just steal your money?