I have tried two item finders - Tile and ProTag Duet.
With Tile, I was actually a Kickstarter contributor, and it was a pretty abysmal experience. They kept changing the date the tags would be sent out, butting right up to when we were supposed to receive them. Which seems okay, but then I couldn't use it with my phone because I had an Android (which not realizing that was my bad)... luckily, i have a husband with an iPhone. Eventually I stopped using it because they added too much bulk to my wallet. We went back to them and then it said we'd have to replace them - which it wouldn't let me do when we transferred two tiles to my own account (because when we started using them again there WAS an Android app). I hear they are developing a thin tracker now (perfect for wallets), so I might recommend it to my husband - who seems pretty happy with them.
With Duet, getting them was even WORSE. I was really looking forward to because able to have a credit thick tracker and the battery just didn't last NEARLY as long as it indicated it would. mostly because it would make the alarm go off on my phone if I didn't have the app open. Seriously. It was horrible. Then I broke the back of the other tracker when I went to replace the battery in it. So I called it on that one.
I might be trying the pebblebee or the Chipolo next because really - it can't be WORSE than either one of those. If Pixies had an Android app, I'd be down to try them also.