Many experts consider it only as a backup method, but in many different situations that is the only method available. Yes, it is only applicable for a medium to small pistols or revolvers, but sometimes we have to compromise. It may be preferable to carry a rifle, but in most situations it is not an option, so we have to compromise for handgun already. And if you cannot carry your 1911.45, still a smaller weapon is better than no weapon.
One of the major reasons the ankle holster is chosen is obviously for concealment. When wearing long pants, the holster is in effect undetectable. It is very easy to get to, especially in sitting position. With a little practice, the weapon can be withdrawn quickly and without warning. There many reasons, you can reach to your ankle while in sitting position. You may feign an itch or pretend to drop something on the floor next to your leg or casually raise a leg and rest it on something.
But the best use of ankle holster is in a car. Your gun will not wedge itself between you and a car sit, it will not get covered by a sit belt and is much easier to reach with either hand than a holster on your belt, shoulder or behind you back. Most importantly, no one outside the vehicle will even suspect that you are in a position to defend yourself, even though you maybe gripping the handle of your weapon.
It is more problematic, obviously to draw a gun from a ankle holster, while standing. There is a number of methods recommended by the experts. Most of them involve holding and pulling a trouser leg with one hand to expose a holster and reaching with your strong hand to draw the weapon. One thing most experts agree on is the necessity of practice. The more you practice, the better you will become. While practice is very important for everyone who wants or needs to learn how to handle a firearm, ankle carry requires additional effort. When ankle carry, the gun is very a long distance from your hand and it takes a lot of practice to become proficient at reaching, drawing, aiming and firing from a crouched and unaccustomed position. In addition, most ankle pistols or revolvers are usually smaller size in barrel length, accuracy becomes paramount.
No different than choosing any other holster, choosing ankle holster is a tedious process usually involving trial and error. There are several factors to consider; weight, comfort, reliability, retention and others. Ankle holsters are made by many fine manufacturers like Fobus, Bianchi, Blackhawk and others. Ankle holsters come in variety of shapes and materials. Choose a holster that is equipped with a soft material, like foam or fur, to protect the ankle. This will keep the skin from chafing. Make sure the holster will retain the gun, not letting it fall out, during walking or running.
You can find an extensive selection of good ankle holsters from different merchants on line or in the gun shops. For example http://www.holsterland.com has excellent selections of ankle holsters to appease everyone.