Recently used KR on our 15 day trip around Europe. It was pretty awesome. A few errors here and there but saved us over $240 vs. roaming on ATT (Used over 2.3GBs of data). $7.99 for 24 of unlimited data is pretty awesome. You can find cheaper for local SIMs, but going across multiple countries its easier to not to have to stop and find local ones. KR has good instructions on how to use it. Worked in Austria, Poland, Czech, Hungary, Germany and Switzerland. Had another phone on AT&T and KR used mostly the same networks with the same speeds.

I got hit with a $10 AT&T charge for the 400kbs of data my phone pulled down before KR kicked in. What a scam.

Posted more details in my blog (in my signature) if you are interested in the full review.