I voted never, but on one occasion I have.
My first GearWrench was a 18mm Mr Goodwrench I bought from AutoZone for some front end work on a Chrysler product I had and they didn't have a 18mm regular wrench at the 24 hour store I was at. I couldn't believe the price (expensive, at least to me, around $20) but it was one of those, had to get it done before morning type things and a socket wouldn't work.
I had to use a hammer on the edge of it to get it loose and it worked fine. Also had to use it to torque it down (again with the hammer, don't know the torque specs, don't care as the car is long gone) but I was amazed at how cool of a tool it was.
Now I don't wrench a lot, and my tool expenditures are very limited with 3 kids, a mortgage (and now a second with an addition) and two car payments. They are really more of a luxury to me, but of any tool I could go out and buy now, hand or electric (i.e. battery powered), these are what I would buy. Now recently Ace Hardware had 4 piece sets on sale for $10 in both metric (10-13?)and SAE (3/8-9/16)and I bought both sets and typically go for them before a regular wrench or a socket and ratchet.
Now keep in mind, I voted never because I don't consider under 20 foot pounds 'breaking free or final torque'. If it's a rusted fastener, I don't use them to break them loose and if it's a pretty high torque, I don't use them to set it.
This weekend I had a perfect situation for my 1/2". I was hanging some 8x8 cedar fence panels on some metal pipe gate frames I had welded up. I used a 2x4 vertically spanning the four horizontal 2x4's that the pickets are nailed to and the frame happened to hit the vertical 2x4s between the horizontal ones. I got some 1 3/4" x 4 3/8" u-bolts and drilled above and below the pipe and ran the u-bolts thru and they stuck out about 3/4" into the 1 1/2" space. It would have been a lot of open end wrenching or fixed boxed wrenching on those eight u-bolts and a LOT of hand cramping with my carpel tunneled hands.
The one thing I haven't found and that I wish for would be able to fill out my collection without repeating what I already have. As much as I wish, I just can't afford to buy 12 and 13 piece sets, I'd like to be able to buy the next 3 or 4 pieces above and keep doing that to fill out my collection.
I'm not a big flex head guy and I don't care for the reversables, I'm okay with just flipping the wrench over. I don't need extra long ones, or twisted handles, double boxed ended ones might be nice as it's two wrenches in one, but the reversable quad boxed ones that each side is a different size isn't my bag. I don't even own a flex head ratchet and the only times I've used one, I didn't care for the handle moving in a different direction than I wanted it to and I didn't have the luxury of the room to hold my hand on the head.
I have the Robo-Grip pliers (waste of money) and a few other gimicky tools, usually as a father's day gift or birthday, but of the last 30 years or so, I think this is the greatest idea to come into the hand tool market.
Oh, and if my name is drawn, I'd rather have a few more GearWrenches to help fill up some spots, if it's possible.