1. Is it uncomfortable?
2. How do you keep the holster from sliding down your leg?
3. Does the gun bang against your other leg?
1. It can be with the wrong holster and firearm choice.
2. Get the right holster and firearm
3. See #2
I carried a S&W Model 49 in a Renegade Cozy Pardner holster for years, (even carried a Model 38 a few times and that was even nicer). It was a perfect combo. Even though it's no longer my daily carry option I liked it so much I purchased another holster just in case I ever need it, (the holster is no longer made and I believe the maker is no longer in business).
It was so comfortable it got to the point I'd almost forget I had it on.
Even though you didn't ask allow me to offer some positives to ankle carry as your bound to get many negative comments, many from folks who have no actual, first hand experience.
Ankle carry is not perfect for every firearm, person or situation but, if you sit at a desk it's very accommodating. Easy to reach and unlike waist carry you never get you firearm and or holster banging on or getting caught on chair arms.
You can remove your outer garment when ever you want. T-shirt or suit jacket, all the same. If you need to take care of business where better to have your carry piece? It ain't flopped over on the floor which can be a filthy situation and you'll never leave it in the stall like some folks have done.
To me it makes perfect sense for a BUG and a lot of the time for your main carry. I've read about folks using it with a Glock 26 or 27. That seems like it would be much less comfortable than an j frame.