Ask HN: Web-based SaaS products with in-app purchase-style revenue model?

Mobile apps that are free to download and which generate revenue through in-app purchases commonly appear to be, or are reported as being, more financially successful than mobile apps with an up-front cost. I don't have any sources to quote there, it just feels like a current trend based on articles posted to HN.

I'm considering if such a model can be successfully applied to my web-based SaaS startup.

My product offers a limited free tier and a set of premium tiers supported through monthly paid subscriptions.

The product carries out automated web testing and presents the user with results with the scope of testing, depth of testing, and permanence of the results determined by how much the customer pays. That's an intentionally abstract description as this topic is not centred on product itself.

I've hypothesised that, for some users, a monthly paid subscription is impractical due to occasional use - the product may provide value on a handful of occasions throughout the year but not on a regular-enough basis to warrant a monthly subscription.

I'm contemplating a revenue model in the style of in-app purchases in addition to what is already in place.

I feel it is a good fit to how my product works - the user could carry out, without charge, a website test and then choose to pay a one-off free to gain full access to the results.

I'm not aware of any SaaS products that use such a revenue model. This by no means implies that there are none. I'm a very small sample size.

I'd like to ask for examples of where an in-app purchase-style revenue model has been successfully (or unsuccessfully!) applied to a web-based SaaS product as well as to seek comment on the idea.

Are you aware of such a revenue model being applied in this way? Have you seen it work? Have you seen it fail?