I'm using the free version of Duo to learn French at the moment, 33 days in. It is good, I'm still at a basic level and yes some words seem a little odd but they do cover the formulation of sentences. The thing is that you are forced to deal with the masculine, feminine and neuter variants of words with French so they occasionally choose obscure words to do that. It is available free so no buyers remorse!
Negative is the free version only tolerates 5 mistakes per day so if like me you have dyslexia or struggle to sort genders and plurals in English, you will likewise struggle when typed answers are required. This isn't very often but is a real stumbling point. It will ping you for just a single letter wrong or misplaced! You can always type the question into Google Translate but this doesn't always produce the answer Duo wants!
That being said, I feel I'm further on in a month with this than I ever got at school or in real life! essentially because it does force you to learn written/read language at the same pace as spoken. In life you can usually get by with a fairly minimal spoken language, especially when the written is not so different you couldn't take an educated guess which loo to use for example!
My plans for the upcoming adventure will require me to be able to communicate with a rural French man via VHF radio to get permission to navigate a canal tunnel etc.