I've always left my ball mount in the back. Had one college student roll into the back of me at a red light once. He already had about a dozen scrapes on his front bumper, so wasn't sure which one was my hitch, but didn't have any damage on my 1500. It was such a low speed, I wasn't worried about the hitch. Had a slight scratch to the paint on my ball mount, but it kept my bumper from getting scratched.
I really like the idea of the sparebumper. Have never heard of them before, so it looks like I have something else to buy for the truck now.
If someone hits me hard enough to bend the receiver or frame on my 2500 diesel, then I'm sure I'll have other issues to deal with.