Based on that cost structure, if it saves the average user 15 minutes per month then it has paid for itself.
I make this argument solely because when it comes to developer/professional tools, tens of dollars per month is a fairly trivial cost.
Additionally, as others have mentioned, I think some of the issue is the lack of a free or low cost personal tier that has some set of restrictions. What those would be for an arbitrary pairing tool I don't know, but it feels really pricey if I just want it available for one-off pairings.
Now, personally, I could sign my OSS project up for a free version, but since I don't need (or want, lol) to pair with most contributors, that feels a bit wrong.
Automatically bumps to the $25 price if you go over.
Unfortunately Teams, while terrible, is sufficiently usable that I don't see being able to persuade my current environment to adopt Tuple either.
I think, if I actually paired outside of work, I'd be willing to spend $5-$10/month just for casual non-commercial use. I'm not sure when I'd ever take advantage of such a pricing tier, sadly.
A limited free trial can be good. But if you make it cheaper or free now, it's way harder to go back up In Price than it is to cut price later.
In any case, Tuple is really great. For us, I think it would become a no-brainer if it had a seat-based model. e.g., we pay for 4 pairing seats a month, and a max of 4 developer can use Tuple at any given time.