Wow, I've been looking for something like this for quite a while. I was using fluxtream, which now seems shut down, but was never satisfied with the view alternatives.
I think it would need some more simple pre-made visualizations or guides that help you make some comparisons. With that, I think the biggest problem is that it's not findable. Even when searching this forum a year ago, I did not find this post!
How would I go about if I wanted to add an importer/connection to another system, like garmin or polar?