I usually use either a SIG P230 or a S&W 642. These days, its mostly the 642 due to the Desantis holster I use. If they made one for the P230, I'd use that.
There are a couple of factors here. One, what kind of pants do your wear? They do need to be fairly loose and baggy, and I find full cut straight legs, of a heavier material, to work the best.
The holster makes all the difference in the world. If its doesnt fit you right, you'll never wear it. Many are very uncomfortable for day long use. For me, the Desantis "Leather Ankle Holster" is the most comfortable I've found and the only one I can wear all day without discomfort. I have a Galco Ankle Glove for my P230, but its not near as comfortable. Now if Desantis will only get the hint.
Gun size is a combination of the above, and realistically, I dont see you wearing a large frame gun, unless you normally wear clown pants and shoes.
One thing with the ankle holsters, they tend to be pretty easy to spot if your looking for them. You have to watch when you get out of the car and especially higher SUV's and trucks. You also have to watch when you sit when in the open and how you keep your legs. The wrong pants and the bulge can give you away pretty quick too, as can the grip poking out the back as you walk ( I wear mine more rotated towards the front instead of on the "side"). Other than the bottom of the holster popping out at a party while your sitting on the couch and put a leg up, most of the others are not a real big deal, but you do need to pay attention.
Your ankle is a daft place to carry a firearm. Too hard to get at in a hurry.
Well.... it sorta, kinda, depends.
With a little practice, it can actually be pretty quick to get to, and you can do it in a couple of ways too. You can drop to one knee or you can draw the leg with the holster up. Both work and both are pretty quick. You do have to use your head with both though, and adjust your tactics accordingly.
It also allows for easy and fairly natural access while driving, more so than a belt holster.
For the most part, they are used with a back up gun. They have their place and give you more options. You just have to be realistic in their use and understand their shortcomings.