This can be a good choice for a backup gun, but you should think about whether it is the *best* choice for your lifestyle. I certainly wouldn't keep my primary on my ankle, unless I had absolutely no other choice.
It is a carry method that takes some getting used to, but it can be quite comfortable if done right. You'll need a quality holster and the right gun, of course.
I keep a Taurus 85 UltraLite in a KL Null ANK. $110, six days from talking to Ken on the phone to holding it in my hand. This was a close second choice to the Alessi Ankle Rig for about the same price, but Alessi had too long of a wait -- and this was a very, very close second.
Hand molded leather, no thumb strap. Retention is great -- I can hold the holster upside down, give it a good shake, and the Taurus stays put. It starts to slip if I sling it up and down *really* hard -- but really, if someone's holding me by the feet and swinging me around like that, it's too late for me to do anything about it anyway.
Many people recommend wearing ankle holsters above 6" hiking/tactical boots to support the weight. I find this unecessary, at least for me. Of course, I wear suits at work, so boots aren't an option anyway.
I put on an over-the-calf cotton/lycra dress sock, then put the holster on top of that. The sock fabric is very clingy, so it grips both my leg and the wool felt backing on the holster. Quite stable.
I keep the holster a bit lower than you'll see in most photos, I find that it tucks into the hollow area between my calf and ankle perfectly. It's angled just right for a draw, and the butt doesn't stick out any wider than my calf muscle.
Of course, with the holster this low (the muzzle is even with and just behind the widest point of my ankle) it is visible when the pants leg rides up (eg, when I'm sitting). I wear another cotton/lycra dress sock (mid-calf length) over the holster to hide this. Dark socks without patterns work best. People have to really be looking to notice the lump.
That said, I'm also careful to strategically position my leg when I'm sitting. Crossing your legs underthese circumstances is nothing short of stupid.
The sock *just* reaches the mouth of the holster, and does not interfere with the draw. It even contributes a bit to stability -- even if things do start to slip, the fabric jams up underneath the wool backing and keeps the holster from falling any further. This gives you enough time to get to a bathroom and adjust things. Anyway, I only had this problem for the first few days, while I was still getting used to the arrangement. Every time I go to the restroom I grab the holster and try to move it around, but now it never budges. Run, kick, jump, whatever -- no movement.
Light slacks will print when walking, or in even a slight breeze. Winter-weight slacks don't have as much of a problem -- though with 30mph wind gusts today I was feeling more than a little exposed. Before summer comes I will have to get the left leg lined on all of my dress slacks, to stiffen up the fabric a bit. Cotton twill (Dockers), denim, etc., don't print at all, in my experience.
Now, all that said, most of the ankle holsters out there are absolute garbage. A good one does not need thumb straps. That thing Fobus makes is a joke, as is Unkle Mike's. The Bianchi holster doesn't look like something I'd trust, though I can't claim to have handled one.
You really don't want to skimp here. Comfort, stability, and retention are all critically important. IMO, the Galco Ankle Glove is the minimally acceptable choice in ankle holsters -- but I, personally, don't like the idea of neoprene. YMMV.
I can heartily recommend the ANK from personal experience. Ayoob, Farnam, and Gary Slider all endorse Alessi. I hear good things about Rusty Sherrick's Ultralight. These all cost $100-$120, compared to the Galco at $60, or the Bianchi/Uncle Mike's/Fobus/whatever from $7-$25.
You get what you pay for.
Photos: I'm pointing at my the point of my ankle in the photo; and obviously not wearing dress socks.