Branding/naming confusion with http://celeryproject.org threw me for a loop.

2% of revenue on top of existing payment processing fees seems steep. I guess convenience has a price and this will be great for shops that want to get going quickly and are not price-sensitive.

Seems like you are self-selecting for small payment amounts. If I had a $100 item I'm not sure why you should get $2 as opposed to 20 cents on a $10 transaction. I believe Shopify used to use this pricing model but changed as they were losing out on potential customers with higher priced products.