Hi,
I'm the guy behind UAV Toolbox, which runs on the Typhoon H/ST-16. So you can read the following with that bias in mind
The H520 is a great flying platform - incredibly stable, especially in high winds that would take other drones away; fast and responsive with very accurate positioning. The motor redundancy means you can loose a prop and not crash, and it's also remarkably quiet, which makes a nice difference from some of the other big birds out there.
There have been some software problems (not unusual in the industry, sadly), but the forthcoming firmware update promises to address those issues. Historically, Yuneec have been pretty good with firmware updates - adding new features to models that have been out for a year or more and steadily improving the tools. Obviously you can't promise anything until the next firmware actually arrives, but the H520 is based on the PX4 controller, so it's pretty robust and well understood.
I couldn't imagine flying a drone without the ST-16. Everything 'just works', with controls to hand and the screen properly integrated. That means no fiddling with articulated arms, no hidden cost of an extra screen, software that is reliable and always there (no unexpected out of memory errors, system upgrades, phone calls from your Mom). It also means you get decent flight logs (which my software uses) and on the consumer model you get FPV video and photos recorded automatically, so you can review flights without having to pull memory cards out of the camera. Basically you can pick it up, switch it on and off you go - no fiddling or fussing in front of a client, and it doesn't look like a toy. Oh, and the battery is swappable, so you can keep on flying all day long.
Yuneec run their company pretty carefully - they've been in business for years, and have avoided the big splashes of new entrants that promise the earth and then disappear. They launched the H520 very softly and have been working on building a solid commercial platform focussing on surveying and reconnaissance rather than promising it would do everything. So there aren't huge numbers of 520's out there, and if you want it for cinematography, it's not the drone for you. They try to work on strong customer support, so if you can get to a distributor and have a test flight, I'd highly recommend it. If you just want to grab something cheap from Best Buy, there are other options.
