I am using the Sierra antenna you questioned, using it on a 2008 Wing, since I bought the bike new. I didn't want to go with the two antenna look.
Because the antenna is a "combination antenna", there are compromises. I only use the antenna for cb use. I never use it for AM/FM. Others have stated
that the antenna does not work well with AM radio. It works fine for the weather radio.
Everyone that I ride with tells me that my cb transmissions are very clear, the best in our large riding group. I am using an Edset headset.
With a dual antenna setup, the AM/FM antenna interferes with the wave pattern of the cb signal when transmitting.
My 2 cents.
Straight Arrow