As of now, I don’t have access to real-time statistics on the comparative usage or effectiveness of Duolingo, ALEKS, Coursera, and QuestionPro.1
References
1Zargoun E. Comparative Study the Role of artificial intelligence and their Impact on Teaching and E-learning Platforms (Duolingo, ALEKS, Coursera, QuestionPro). African Journal of Advanced Pure and Applied Sciences. 3(3):263-274. https://aaasjournals.com/index.php/ajapas/article/view/795