This is rather a nice minimalist wallet and as others have said, thieves often just take out the cash and ditch the wallet, but if you lose it, having the tracking device would be a boon and help you get it back. However, I would much rather have RFID protection to stop my cards being scanned while I still had the wallet and this would render a tracking device in the wallet useless!
Much as I like this, I will wait until the tracking devices are thin enough to sit in the outside of the RFID protection material and then I get the best of both worlds!