It depends what kind of learner you are.
Osmosis seems to work well for people who like little khan academy style, cartoonish videos. They personify the cells, organs etc, and use little memory hooks to help you remember things. It also has this cool function where you can import your class powerpoints and it will automatically link buzz-words it finds to helpful videos on the subject.
Firecracker is geared towards the more brute force style of learner. Their Anki-Style QA system is great for spaced repetition, you don’t have to make your own cards, and it contains all the info from first aid and then some. A major con is that the amount of info on firecracker is almost insurmountable, which means you could miss high yield facts buried in all low yield junk. Their explanations are generally more bare-bones - just bullet points on a page - although sometimes they link out to osmosis or khan academy’s videos on a topic.
Overall I tried both and liked ‘cracker way more, but neither is perfect.
