As a finnish person I can say that this is bullshit. I almost find it insulting. First of all, Simo is a finnish name for males. The "real" Simo Häyhä (because yes, he was a real soldier who fought in Winter war) was a male. I have no idea why they made him a female in the manga.
I don't think I have ever disliked a manga this much. Especially because when I heard that there would be a manga about winter war I was really excited, so this was just a huge disappointment. At least the art is good.
Would I recommend this to anyone? Well, maybe if you like war mangas and don't really care about historical accuracy. But even then I'd suggest that you just go and find this in your local library, it's not worth the money.