I was pleased with the build quality, the ergonomics are thought out so that no display is needed in principle. Even a cursory glance at the control panel is enough to know exactly the current flash mode. I took it on A77, compatibility is on top. Also works great wirelessly. On a set of NiMg batteries for 300. took about 300 shots, the reload speed has not changed much. To install on the A77, I had to order an ADI-AMA adapter for 990 from the Sony Store. The adapter practically merges with the