How many stores have you visited recently that have turnstiles? You've probably been in more that are using a variation of this tech.
There are a few companies offering it as a commercial product, and yes there are people that want to buy it. The value is not just knowing how many people are in a store, but where they are going, what they are spending their time looking at.
They've been able to do that long before invasive solutions like this, or computers, even existed --- turnstiles.