It depends. If the portrayal of the yandere girlfriend is done in an interesting and nuanced way, it could be appealing. But if it's overly stereotypical or one-dimensional, then no.
A gift from her in a yandere manga can have multiple meanings. It could be a sign of the yandere's obsessive love, an attempt to control the situation, or a way to create drama and tension in the story. Sometimes, it might even be a red herring to mislead the reader.
The ending of Girlfriend Girlfriend manga is quite complex and bittersweet. The characters go through various challenges and their relationships evolve in unexpected ways.
Well, such a girl is often obsessive and possessive. She might go to extreme lengths to keep the person she likes close to her, sometimes even using violence or threats.