The environment is sort of like a game or quiz. This is a big plus.
But here is the con. Fluencia is not free. Much like Babbel, Fluencia gets you hooked and THEN throws you their pitch. I'm moving through the course, enjoying myself, when suddenly a box pops up and informs me I only have a few more lessons until I will have to pay.
What? Yep, a hundred dollars a year. It's less expensive than Rosetta Stone, but I'm not crazy about the fact that they tried to trick me either. Are these courses afraid that if they don't state that they cost money up front we won't bite?
Maybe it's because free language courses are the wave of the future with courses like Duolingo leading the way. Even ad based courses and courses that offer a basic account tend to do better than totally paid courses.
If you are learning Spanish go ahead and try Fluencia. You can at least take the first fifteen lessons. If you like the style and can afford the subscription, it's totally worth it.