From the reviews I've read, this looks like the perfect software for what I want to do. The problem is that I will only need to use it about once a month for my intended purpose. This makes a £24.99 price tag really hefty. Could you consider a light-user price, where the app limits you to say once a month or whatever? I would pay for that.
It's unfortunately not something I'm planning to do. However, the trial version only counts days you're using the app, so you could get around half a year of free use out of it, given your estimated usage pattern.