If you like that method that's fine and all, in my opinion, no money needs to be spent at all to learn a language. Some people hate learning grammar ideas, and prefer to just learn vocab. This is not me. To learn all the grammar of Russian through the free magical power of the internet, that'd that like a month, maybe 3 with memorization time included. When learning with payed all-in-one products (as well as classrooms), they like to hide complicated concepts from you, and lie, so as not to confuse you, and explain bigger concepts later, once they've set them up more (such as declension, formality, or literal translations). On the bright side, learning vocabulary and pronunciation through those methods is great, while much harder through just internet articles.
Anyway, you should be fine even if they do share a lot of vocabulary between each other. All that really matters for a long time is the 200-700 most basic words, which those lessons are probably targeting.