The spray on bed liners are smooth until texture is added to them. I checked out the Keel-x product put on by the guys that do Line-x. It's a nice option, but it doesn't add the cushion that a Keelguard or Keelshield would, so I am still shopping for those.
The line-x would still protect from scratches, but not impact. There should be no drag since the texture would not be added on the keel.