Just spent 10 days in Europe, through Zurich, Paris & Amsterdam using a TEP mifi unit and wanted to say that for my wife & I (and our assorted devices) it worked about as well as I'd hoped. A full charge on the mifi lasts around 8 hours so if you're out and about all day I'd recommend turning it off when you're not using it to conserve the battery. I never ran out of juice but it got down to the danger zone a few times.

Service was 3G at best, and oftentimes much slower, but it works for maps and checking Twitter, uploading to Instagram, etc. Can't really complain for $9 per day. Ordered the unit a week before my trip and got it in like three days. Meant to return it transiting home through LHR but missed the fine print that said the return location was outside of security. Emailed them and they promptly responded with a new mail label to use when I got back to the states. I would definitely recommend TEP!