I'm not familiar with their product, is their back-end choice going to limit their customers?

I think that a lot of developers that didn't start with front-end work find Javascript disgusting, maybe this team is in that group. When I worked at a consulting firm (that used a lot of C#) and we talked about node.js when it came out, everyone agreed they hated the idea of having to write more yucky JS than they had too. I think node.js was high on hype for a while and is less loved (esp outside of CA) than you might expect.

I've ported node.js apps to Go 1.0.1 and even back then the result was better performing, used less memory, about the same LOC and IMHO much cleaner, straight-forward and maintainable code.