The manufacturing of aftermarket mounts for Garmin devices has become something of a cottage industry. K-Edge, SRAM, 3T and others have all developed novel ways to affix your favorite Edge or Forerunner to your bicycle. Tate Labs actually claims to be the first player in this market, and others have corroborated that claim (and although I have no reason to doubt them, I can't independently verify it). In concept, these are pretty simple devices; they involve attaching a proprietary Garmin mount onto a round bar clamp or other component.
The Bar Fly is exactly that, and comes in two flavors; one for oversized 31.8mm handlebars, and another for aerobar extensions. Reviewed here is "Version 1.1" of the Tate Labs mounts. These have wider compatibility with Garmin devices than the original Bar Fly, and work with both Edge and Forerunner devices (more on that below). We set them up on our own 22.2mm Gamma bars, where they worked very well. But they'd probably be fine on the 22.0mm standard as well. The Bar Fly is made of injection-molded plastic, which is a good material for the job. It keeps things light, and at the thicknesses used, it's plenty stiff for mounting a computer. Both versions of the Bar Fly weigh in at exactly 17g, including the bolt.
Another advantage of plastic construction is that because plastic is flexible, you can get away with using just one clamping bolt rather than two. The plastic flexes to open around your bar, and then the single bolt clamps it down. I like that simplicity. For reference, this is exactly how SRAM's mount works as well, but SRAM only makes theirs for OS bars, not extensions. To my knowledge, there aren't any other injection-molded options for an aerobar extension mount. There are 3D-printed mounts available, but I'm not sure I'd trust a 3D print with that kind of job (they tend to be brittle). So the Bar Fly does the trick very nicely.
The Bar Fly's other claim to fame is that it only takes 1/8 of a turn to engage or disengage your computer, compared to 1/4 of a turn with other mounts. Not really a big deal either way in my opinion. BUT, it has a greater implication for compatibility, which is pretty important. You see, while the Garmin mounts used on bikes are all roughly the same, they are oriented differently. The Edge series has them oriented in portrait, while the Forerunners are in landscape. With 1/4 turn mounts, you'd have to set the mount up for one orientation OR the other. And if you switched from using an Edge to a Forerunner, you'd have to uninstall, rotate, and reinstall the mount to get it to face the way you want. But with a 1/8 turn mount, you can use either class of device, without needing to touch the mount. You just change which direction you rotate your device when locking it into the mount. It's a very clever, elegant design, and according to Tate Labs, the only mount on the market with this feature.
All that's left is the price. The Bar Fly comes in at $25 retail, on par with the competition. But the Bar Fly TT is $40, a little pricier. But then again, the only competitive products I'm aware of for extension-based mounts are at least that expensive. Personally, I prefer an aerobar-mounted computer, because you can put the computer right behind your hands, forward of a BTA mount. Base bar-mounted computers are virtually impossible to see while in aero. So I like that the Bar Fly comes in an extension-based version.
And that's about all there is to it. Tate Labs has done a great job with the Bar Fly mounts, and they work well.