I got a hexamid solo with netting because it was the lightest shelter I could find which would protect me from bugs and be fast and easy to pitch well. Shaped tarps tend to be easier to pitch, but you have less options in how you pitch. As to using the hexamid without a bivy… it's possible to use without a bivy. In a bad storm, especially with blown rain I would want either a bivy, a door, or the extra beak… mostly because I move a lot when I sleep, I overheat so my quilt is often open so it extends beyond the edge of my sleeping pad. It would be possible to manage without one of these IF you don't move much when you sleep and you use a ground cloth which is small enough to it doesn't collect the blown rain, but keeps your quilt / bag from touching the ground.