I get the task pricing motivation: you want folk to pay for how much they use, not a flat rate, because if they are freelancing why spend a flat fee for variable use. One of the reasons I don't use Lightroom is that I only take lots of photos a few times a year, and I feel stupid paying for a month in which I don't use it.
*However*, this alternative is pretty weird. Think about it from the perspective of a software developer. Would you really want the granularity of your tickets dictated by a pricing model?
I remember when I set up integration between GitHub Issues and some external ticket system, I've introduced infinite loop and issues being created on both sides. I'm glad that I didn't pay per task.
On the whole it's also conflating different incentives. You don't typically associate your costs with _how_ you're using your tools, at least you don't want to. It creates a bad (or perverse) incentives to change how you work in order to minimize costs, you're rewarding your users to use your product less.
I have seen an at least 10x variance in how people document their work in tickets. So 1 or 2 cents per "story" for some becomes 10 to 20 cents per "story" for others.
For me that just feels like a weird external factor. If it doens't bother you more power to you.
*However*, this alternative is pretty weird. Think about it from the perspective of a software developer. Would you really want the granularity of your tickets dictated by a pricing model?