Henrietta barely survived a brutal attack that killed her family. 'Rescued' by the Social Welfare Agency, her injuries were repaired with robotic components and she was brainwashed. Lost with the memory of her family's deaths was almost every trace of her own humanity. Now, she is an extraordinarily lethal cyborg assassin, obediently working with her handler Giuseppe to carry out her deadly tasks. Despite her conditioning and programming, Henrietta still has the heart of a young girl. She has not completely forgotten how to love, yet the very emotion is contrary to her training and programming. Can the Gunslinger Girl survive? Can she find peace in a struggle against her very nature?
The quality of manga readers can vary. The uploads are often done cheaply or as a serious hobby by a collective. Be aware that sometimes licence hasn't been given but the sites noted above, Manga Fox in particular, are extremely careful about adding and pulling mangas according to license agreements. So you shouldn't have to worry too much about the material being pirated. There are also translated works and non-translated. Amongst the translated works you will find that the quality of translation may vary according to the skills of the translators. Usually the works are perfectly readable anyway, with only a few added or dropped words or a word in the incorrect tense or with/out plurals. But sometimes the text becomes gobbledygook. In which case, either seek another version or give up and buy an official copy once a printed translation comes out. The other issue of note is you may need to expand the screen to read the text easily as sometimes the scans are minimised a little.
I find that if a page doesn't download properly or some other issue occurs (too slow or someone ordered the pages incorrectly etc.) with one reader then skipping across to another reader and picking up where I was is quite easy and rarely annoying.
Otherwise, enjoy and watch out you don't get too addicted you forget about the necessary things in life.