This little orange "egg" as my kids like to call it, is very similar to a Beauty Blender, but without the price tag. Do I think this is needed to apply foundation? No, BUT... It is going to make a huge difference in the application. This will help smooth out your foundation and make it less "cakey." I have tried a few that don't have the flat edge, but you almost need that edge for certain areas of your face. I definitely prefer this one to others. It is sturdy, but not stiff. A common mistake people make with these sponges is not getting them wet before hand. Make sure the egg "grows" quite a bit under the water and then squeeze it out and I always grab a towel or washcloth afterwards and give it a squeeze in there as well. This will help with a smoother application when applying your foundation or concealer.
If you are are still not convinced, here are some others that I have personally tried and do like. I just wish they had a flat side. I use that a lot. But these are equally as good as the Beauty Blender without the Price Tag!