This will be my first review on MAL. I chose this Manga since it's a spin-off of, what is at the time of this writing, my all-time favorite anime. There will be spoilers in this review for the original Madoka Magica, as it would be ill-advised to read this spin-off without first seeing the original show anyway (or reading the manga adaptation if that floats your boat).
I'll try to avoid spoiling anything from this manga itself, but there may be some spoilers.
The story is fast-paced, fun, dark, and not without some all-around good action. That said, the ending and the final product don't really
add a whole lot to the Madoka Magica universe or contribute to the Madoka franchise's world-building very much. It's also a pretty short story and the ending isn't much of a surprise either. The enjoyment is in being along for the ride and seeing how things play out similarly and differently to the original story.
Nothing much to say here except that the character designs and backgrounds match up with the show pretty well.
Madoka's cast of characters are easily my favorite of any anime/manga series. In this story we get to see a different side of a lot of characters. Madoka isn't as naive, due to being taken back in time WITH Homura. Homura is more compassionate due to being teamed up with Madoka. Kyubey's evilness and trickery is much less ambiguous than the anime as he is directly out to thwart Homura and turn others against her. While I enjoy the morally ambiguous, darker shade of gray version of Kyubey the most, this was a fun change of pace. Sayaka was the most different to me, her misguided hostility and vengefulness towards Homura was both fun and sad to see. We also see Kyouko behave more compassionately towards everyone BUT Homura, the one person she cooperated with in the anime.
It was a very fun and decently interesting read. But it doesn't have any major impact or tie-in into the larger Madoka universe other than being just another failed timeline.
If you're a hardcore Madoka Magica fan, or aspiring to become one, this is definitely worth a read at some point, but I wouldn't put it at the top of the priority list. It isn't crucial for understanding the world of Madoka, but it's short, sweet, and plenty entertaining.