I have one reader connected to my ipad. Got it for free so I had to try it. I have accepted only one payment so far so not much experience about it, but some comments:
For private individuals a facebook account is needed to accept payments.
The legal agreement is a mess, they even warn that your data can be transferred to countries where privacy laws are not in par with european standards and data is stored for 7 years
Location of the transaction is stored and cannot be turned off, it's unclear why this is needed.
They seem to comply with PCI data security standards but are not audited (yet?)
The customer must sign the transaction on the ipad screen with finger (even harder with iphone). it's very hard to check that to the signature on the back of the card. also the customer must type his/her email on the screen if they want a receipt (there is no receipt printer). So each transaction takes a long time.
So it's good for selling at fleamarkets and such but for serious business it's no match for a payment terminal. Also if you don't already own iphone/ipad then it's also more expensive.