I added them to my RK when it was new. Saved tons of damage from occurring when kids were on tricycles bumping into everything. I also have a bag guard bag attached that has a water bottle holder and a small pocket for spare sunglasses etc. Very functional.
First thing I did when I got my RK was add the saddlebag rails -- my dealer gives a scratch-and-win ticket with every new bike, and my ticket was for $250, so I got them almost for free. It gives the bike the look I like. Other add-ons to my bike are on or off depending on my current mood, but the saddlebag rails stay on all the time.
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..... my Road Glide came w/nuthin' back there
.... but the 2nd hand guards from ebay kept my stretch bags safe when she went down on a friends gravel driveway.