You shouldn't feel bad about buying an (expensive) license if reverse engineering a hobby of yours. Computing is such a cheap hobby it's OK to splurge every once in a while. And there's a good chance the skills you build end up paying dividends later.

Compare computing to other hobbies. Anything involving cars/boats/motorcycles: expensive. Woodworking, metalworking or anything else that requires a shop: way expensive. It's easy to spend thousands upon thousands on most hobbies every year. In contrast with computing you can do almost anything with very basic tools.

It's great when there are high quality free tools out there. But most of the time these free products get abandoned or are left unfinished. It's hard to get a community of volunteers to do the schleppy maintenance work for 20 years when the product is already feature-complete. And that's why we should be glad there are commercial alternatives, even if they're a bit pricey.