Only use I can see for these outside of actual parenting (and even then its extremely lazy like a parent is not bothering to check on their child and leaving it to an app to alert them), Is for long distance AB relationships or people without the physical ability to feel or check their own nappy.
They are an interesting idea and all but for an AB it's much better to have the personal experience when a carer actually does a diaper check (patting bum, pulling trouser waistband back etc. rather than just looking on their phone. but for those with a friend/partner/carer that is mostly online it could work as the signal can be sent to their phone to alert them you need a change and they can call/text you to do it.