I have no problem paying for apps that I use and that create value for me. But the cost needs to be proportionate to the value -- and this app doesn't even come close.
At more than $200 a year, this add-on would cost more per month than my Google Drive and Office 365 subs. I can't begin to justify that for a service that I would use only for myself 95% of the time -- and even then, rarely more often than a few times a week.
It's bothersome because it's inexplicable: The developers are, without a doubt, leaving a lot of money on the table with an inflexible and unrealistic pricing model. I could see this getting a lot of traction with a couple of lower-price tiers, especially one that allows SMS messages only for the subscriber's personal use, rather than for invitees. I guarantee you 99 percent of those users aren't paying $19 right now. And if the devs think a low-price option would cannibalize their existing customer base, they might want to book a return trip to Planet Earth and rethink their assumptions.
(For that matter, why not add an enterprise tier with custom pricing, volume discounts, and perhaps additional management/access tools? Big customers are no more likely to accept this ridiculous pricing than smaller ones.)
I don't know what the developers are thinking, but right now they're screwing up their business model so badly that it's downright embarrassing. Here's my invitation: Hire me to sort out your product offerings and pricing, give me a modest share of the revenue I unlock for you, and let's all make some money :-)
Or, you know, keep this up and don't make money. That's easy enough to do.