It's losing some popularity now that companies like Arri are making better cameras, but that's been an industry leader for years... Any DP would be insulted by the accusation that RED is a "vanity brand."
I only learned about RED after all the hype with their first digital cameras (that all the studios were helping to hype)
When it comes to cinematographers, the best tool is what they use. There's no choosing a camera because you look cool next to it...
Now there are cameras that have all or most of the features of RED, but more elegantly designed. The RED is kind of like a small PC that you can mount a lens to.