We don't own any, but only because we already have a fireplace on our patio that works the same way. They have them at many ofthe restaurants in the area, though, and they seem to do a good job. I've recently gotten back from my sister's wedding in Michigan. Their reception was in a large event tent on their property and they had two 7 or 8-ft. propane heaters in there for added warmth. My chair at our table was actually right next to one of them and, although it was warm to the touch, it wasn't dangerously or uncomfortably so. I was initially concerned about that as there were small children at the reception. They were also quite sturdy. I checked and found it would take quite a bit of effort to tip one over. I have no idea how much propane they held but they kept the place nicely warm throughout the reception . . . although I do have to add that the combined 100+ warm bodies of the guests also contributed to that warmth (LOL).
Lynn
Here's a pic I took inside their reception tent. In it you can see one of the heaters and part of the other:

I also don't own one....but my son, who loves to entertain outside, has 3 and a propane heater that acts like a coffee table with a grate and hot rocks in the center.
He has 2 7 foot tall ones, a table top version and the one in the table like a fire pit.
The most expensive was $150. The 2 tall ones take a standard propane tank like your grill does. The table top one and the coffee table one take what they call a "pancake" which is a smaller tank, half the size of the one you use for your grill.
They will burn all evening....and then some. All but the coffee table one are adjustable...you can get more or less heat from them. One of the tall ones has a table that sort of fits around it where you can set your drink.
He bought all at either Menards or Home Depot...or possibly Lowes. The oldest was bought on big time fall close out 7 years ago and still going strong, as of last spring. It's showing a little rust here and there, but it heats well and at night you don't see the rust.

We bought one at Costco about 10 years ago...defective, so returned it & got one at a local garden furniture store. I have to say, it really is nice, esp. here in the PNW, where summers aren't always that warm. I can't remember what we paid, but it was more than Costco price, but not extravagant. The brand is Phoenix Professional Patio Heater. Like Lynne said, it is heavy, but has wheels to help move it around, and the weight helps it be stable. The tank seems to last quite awhile, but we don't use it all the time. Pretty easy to start with a switch.