This a just a really great app. I am a programmer, and I probably spend about 50% of my time on my iPad in this app. It is just that good. The developer is talented, not to mention both friendly and responsive if you reach out to them. I bought this app many years ago now, myself and I have never once regretted my purchase. I only wish all the software that I used on a daily basis was developed with the same level of attention to detail and quality.
If you want to encourage quality software development, the kind which comes from an artisan and not some megacorp, you are going to want to show that is how you feel by purchasing this app. I really do not see how you could possibly go wrong by doing so.
I'm just being honest; facts.