Here are my thoughts on this.
Allow kids to become independent by degrees like they're supposed to...until that mythical time when they get their own flat and only call you now and again, mostly when they need money to take the cat to the vet. Look, I don't necessarily take my own advice but hope the kids will eventually get to that mirage-like place.
Sensible bit of information - the vast majority of child abuse is carried out by PEOPLE YOU KNOW. In other words, your child's ability to trust you as a parent and tell you that Uncle Joey asked them to do something bad the other day is vastly more important than snooping. Family members, parents' 'friends' and acquaintances are more likely culprits and aren't going to be deterred by this kind of thing since you already know the kid's at Uncle Joey's house, right?
This kind of device makes parents lazy and probably increases the chances of the kid being snatched anyway. 'Oi, where's the kid? It's probably nipped off to the butchery section to watch them chop up the pigs again. Never mind, it's got that squeezy thing on.'
I think it's just a great trial for other related snooping technology - being financed and then carried out for free by paranoid parents.
Oh, and a random story - one of my kids was a total runner around the age of three. Got almost lost once in Woolies (couldn't choose somewhere tasty obviously) and after that I purchased a kid leash. Child wore it three times then told me it was no longer required - had learned that the ability to explore is best curtailed by self and not dog-style lead. In that total maybe of two hours I had about 10 complete strangers march up to me and tell me I was a disgusting parent....eh? Same kind of demographic I'd guess as the ones who are interested in this snooping device. I think it's probably an 'obvious' vs 'underhand' style of parenting but I'm clearly biased.