When Panasonic offered their first set of 4K prosumer camcorders last year, the chief difference between the two was a second camera for picture in picture recording. The $899 and $999 models scoot a bit further apart in 2016--along with offering the twin camera, the Panasonic WXF991 also offers an adjustable viewfinder.
Camcorders with viewfinders are hard to come by, and the feature makes it a bit easier for shooting in bright sunlight and many simply prefer composing their shots with a viewfinder over the LCD screen. The viewfinder is adjustable to different angles and makes a nice addition to the camera.
The WXF991 also adds what Panasonic calls "cinema effects" which roughly translates into a slow motion feature and a dolly zoom effect.
Besides the viewfinder, twin camera and cinema effects, the WX991 is very similar to the VX981, albeit slightly heavier from the extra features. Video is recorded in 4K at 30 fps (in MP4 format only) or at 1080p and 60 fps. Even still pictures have a high 25 megapixel resolution. That's combined with a nice 20x optical zoom and hybrid image stabilization system. A five channel mic helps capture sound pretty well without extra equipment, though there is a mic port for expanding the capabilities a bit.
Despite offering advanced features like manual modes, the WXF991 is a fairly compact camera weighing less than a pound. A control ring around the front offers more control over those advanced settings. Outside the adjustable viewfinder, there's a 3" touchscreen too. The battery life isn't the best, but offers about an hour of recording time, less when shooting in 4K. Wi-fi is a nice feature as well.
The Panasonic WXF991 is a solid choice for 4K. If the new viewfinder and cinema effects don't really catch your eye, you can find a deal on 2015 4K models inside our best 4K camcorder list. Or, try the VX981 for about $100 less without the viewfinder or twin camera.