It's an extremely professional video editor that's been used in several Academy Award and Emmy winning movies. Some notable movies that used this editor in production include The Wolf Of Wall Street, Pulp Fiction, and The King's Speech.
Lightworks has the widest native format support available in any professional NLE. MXF, Quicktime and AVI containers, with almost every format you can think of importing natively without the need for transcoding, from ProRes, Avid DNxHD, AVC-Intra, DVCPRO HD, RED R3D, DPX, AVCHD (with AC3 audio), H.264, XDCAM EX / HD 422, all on the same timeline in realtime. Check out the detailed Tech Specs for a full list of supported formats.
The only possible concern you might have is that it's not technically open source yet. There have been plans to make it open source since 2010 but there has been little progress in the last five years. According to the site's FAQ:
Once the Linux and Mac versions are released the source code of Lightworks will become available. We cannot give a date when this will happen, but announcements and updates will be regularly posted on the Lightworks Forum
It's worth noting that the Linux and OSX ports were officially released on August 29, 2015. In any case, this might be a cause for concern if you feel strongly about open source software.
Currently, there are two Lightworks versions, the Free and Pro versions. However, they are essentially the same, except the Free version has limited export options. You have 'full editing power', but export options are limited to MPEG-4 (Web, YouTube and Vimeo) at 720p resolution. This might be a deal-killer for you if you're looking to use this in a professional setting.