Think of self defense as a life long pursuit of collecting the necessary tools to keep yourself and loved ones safe and Aikido as one tool in a collection of tools to be used for self defense.
If you need protection immediately, I would get a gun and learn how and when to use it. Then let everyone know you got a gun and you know how to use it.
With respect, its this kind of talk which puts some people off of aikido. "Aikido is a lifelong persuit", "some techniques will take 20years to learn", "what is the definition of effectiveness"
It's not a hard question to answer, and i would answer Toms question as NO. If you're looking for a martial art to use purely as self defence. Aikido personally is the last one you should go for. Due to the amount of time it takes to grasp as opposed to something like Boxing, Kickboxing etc.
However if you're after something with a bit more spirituality to it, and something that will craft you over many years to become more aware to situation as well as an extra little tool in your belt if you ever do need to defend yourself, then Aikido would be good for you mate.
But i wouldnt recommend Aikido for instant basic self defence, take up something nice and simple and easy. Like one of the arts mentioned above.