Seeking advice and feedback about pricing plan options on power-ups/addons

Hi, IH community!

I wanted to discuss what would constitute a fair pricing and pleasant experience for the users of a paid power-up or addon.

Disclaimer: I am part of a small team developing https://assista.io - a time-tracking bot for Trello

When we started developing the power-up, we wanted it to be the most reasonably priced time-tracking power-up on the market. We introduced a concept called "fair billing" (https://assista.io/pricing/) where we only bill users who actually interact with the bot in a certain way. All other power-ups are billing users either "per board" or "per user of the workspace" which often feels too limiting in our experience. The reason is if my workspace has 20 users, but only 5 of them actually track time, why should I pay for 20 users when I can only pay for 5 who actually need the power-up? On the other hand, this makes the billing and accounting a bit unpredictable, because this month only 5 users from my team might be using the power-up but next, it might be 8 or 2 so suddenly the invoices per month are always different and it's a bit of a hassle to budget this or to do accounting for this.

In your opinion, should we stay with this "fair billing" model or convert it to the more widely used "pay per board" or "pay per workspace member" alternatives? We would definitely increase our revenue if we do that, but our main company value is "fairness" and this doesn't feel too fair.

What do you think? Do you have other suggestions about how this should work?

Thanks!