I understand your point, however I think the idea is validated by looked at google search results: 40.000 people look for exactly how to compute their BMI. I al

I understand your point, however I think the idea is validated by looked at google search results: 40.000 people look for exactly how to compute their BMI. I also saw that there were several sites built around the purpose of calculating your BMI, however I think they are executed poorly. So there's a market for it, even if it's only to make passive income. To justify spending 200 euros: 200 euros is really not much in the grand scheme of things and considering the above, I think it's worth the expense. When asking for links and you have a good looking site, your requests are more likely to be answered than if you have a garbage-looking site. Regarding whether it's a wise investment of my time, it's harder to say. There's the time developing it but also (mostly) marketing it, link building etc. I think at some point you have to go with your guts, you will never have all the data you wish at the beginning. Then if it works really well, I can look into adding more features, more calculators, more content etc...