Ankle holsters suck in every possible way. That being said, I have used them extensively in the past, without the calf strap. In my experience, they tend to bruise your ankle right where that bone ball sticks out if you insist on having a 3 o'clock placement. I settled on more of a 4:30 placement. Nearly impossible to conceal when your pant legs ride up to sit, forget about crossing your leg. I mostly overcame these faults by wearing a thick black sock over the holster, and keeping my hand over the sock/holster. Also get your pant legs tailored a bit longer.
thanks for the info everyone. It is good to know about the calf strap.