Inernal or external, doesn't really matter. For internal though you would need extremely expensive memory cards as the file sizes and bit rates are huge. With external it's cheaper, because you can write it directly to a ssd, which come in way bigger capacity and much lower prices.I'm not a video guy but would someone explain why external RAW is a big feature?
On top of that, if you're shooting video in raw, you're going pro anyway and in that case you'll ALWAYS use an external monitor, like the mentioned ninja V, which is also an external recorder using ssd drives.
I guess you know what RAW is. It's the same as RAW in photography. It allows you to shoot "iso-less". You can change your exposure (ISO) and also the color temperature AFTER you shot your video, in the post.
As I said, the difference between normal video and raw is the same as in photography. It's like shooting photos in jpeg (normal video or flat profiles, like log) and then you got RAW which gives you all of the flexibility to regain your shadows or your highlights without losing any detail. Same for the temperature. You basically use your camera's sensor capabilities to its fullest extent.