Do you think that the Mango language learning program prevents fragile understanding?
Actually, I think precisely the reverse: it is likely that the Mango system leads to fragile understanding.
Fragile knowledge is based on simply learning superficial details without deep and sustained analysis, understanding, and application of concepts. Because it is superficial and generally rote learning, it is quickly forgotten.
Because the Mango system offers quick access to useful phrases, but no sustained understanding of the grammar of a language, the knowledge obtained is of the superficial type that leads to fragile learning. While this is not a problem for travelers who are spending a few weeks in a country and want to be able to order dinner or ask directions, it does not lead to a deep knowledge of a second language.
If you want to obtain L2 fluency, university language courses, which are highly interactive, include both speech and writing, balance grammar with conversation, and are designed based on the latest in language acquisition research, are a better choice.