Well, my car has the blind spot monitoring. And I think that it is not all that it is cracked up to be as it could potentially lull someone into a false sense of security. BSM should never be used instead of turning your head and looking at your mirrors.
With that said, the system does work well. However, I angle my mirrors out farther than many people do. This gives me a really good view of traffic around me with the generous Renegade mirrors. I can see a car or motorcycle before the BSM detector "sees" it. Too many adjust their mirrors so they get a good view of the side of the car they are driving.
One annoying aspect is if you put on your turn signal a little early to change lanes while you're passing a vehicle (normal traffic merge), the BSM will beep. I often put my turn signal on ~5 seconds before I need to if traffic is heavy to let others know my intentions. Occasionally it will beep in error while making a turn if the conditions are just right.
It's not really necessary in my opinion. Is the $600 price tag worth it? Well, you do get security bundled with it so it may be. And if it is too annoying, you can turn off the beep sound (I have left mine on so far). The amber light will still light in the corner of the mirror where one should be looking anyway.