Software:
o) Easy to use
o) Low development costs
o) High security

Pick any two...

Sounds like the story got Waylaid...

I've heard stories here and there that banks are trying to make card holders liable for suspected fraudulent charges because the transaction was supposedly done using the chip and thus the bank says the card must have been present at the point of sale. However, there are many web sites and videos that describe how the chip system has been hacked, but the banks seem to be "officially oblivious" to this fact. I suspect the whole chip thing wasn't a security feature that the banks wanted to help protect their customers, but a way to pass liability for fraudulent charges back to the card holders and vendors instead of covering those charges themselves.

Easy as iMessage to use, works on the devices you mentioned (though no web client), and has good security.

You can restore the laptop to exactly the way it was before you loaned it to someone with a tool like sandboxie, so then it doesn't matter what they do.