For a cheaper substitute, try a Mini Maglight.  They are starting to make and sell them with LED bulbs nowadays.  I think mine (with a standard bulb) was $9.99 at Lowes.

When you're stuck someplace like NYC or NJ, carrying items like a whistle, a knife, or some sort of striking object that does not appear to be an object designed for striking, makes sense.  I always like to consider, though, effectiveness and going to court later. 

If I'm in a situation where I'm carrying a whistle, the chances of my being able to flee towards safety seem to me to be better than being able to draw attention of others to assure my safety or scaring the BG off.  A whistle to guide the cops to me after a shooting doesn't sound like a bad deal, though; on the cell phone, I'd tell the dispatcher, I'm the guy blowing the whistle like crazy.  It might help keep me from getting shot by Officer Too Young. 

In court, what do you say when the plaintiff's attorney (BG or BG's family) asks:  Why didn't you use your whistle/knife/pepper spray/etc; was it really necessary to shoot this poor boy?  How do you answer why you didn't use something besides deadly force to deal with the issue? 

That doesn't mean, of course, that you should not carry anything else.  It just means that you need to think through how you're going to deal with various scenarios and how to "prep" your attorney to ask you the right questions before plaintiff's attorney does so you can inoculate the jury. 

BTW, a small flashlight is often as effective as a roll of nickels in a fistfight and also works well as a striking implement when the end is used.  That's why I like the Mini Maglight -- it's just about the same size as a Kubotan stick. 

JMO, ICBW.