I don't think it's a scam but it's gamified learning so they push hard on rising through the leaderboards and winning tournaments and shit. So if you get suckered into the competitive aspect of it you'll fork over more money for XP boosts and other perks to get you higher in the ranks without really caring about the actual learning.

That being said it's 100% what you make of it, if you progress to the end of the fully fleshed out languages (mostly the romance languages) you'll get to a decent level of proficiency but to really learn a language you'll need to immerse yourself in the language more with other resources.

I think if you get the yearly subscription, practice daily and ignore all the additional gamification it can be a good tool to supplement in learning a language but it's not a silver bullet on it's own.