As of 2019/05 - Tweet your questions.
Why are users allowed to mark challenge as completed?
Majority CTF-based challenges require you to use certain keywords or patterns in order. This may prevent you from creativities in achieving the ultimate goal of bypass. CTF key is required wherever possible.

Is your platform differentiated from PentesterAcademy and PentesterLab?
This platform is developed and updated at own free time. And it is never intended to compete with or fill potential gaps of full-fledged world-class PentesterAcademy and PentesterLab platforms. I enjoyed those immersive labs and got my hands dirty with them to avoid all possible overlaps not to re-invent the wheel; for example, PentesterLab focuses on challenges that are based on CVEs, strenuous crypto cracking and technology stacks such as Rails. Anyway, even if there was an overlapped challenge somehow, this would definitely be by accident. After all, practice makes perfect. It's just to make you better.