Obviously if it's fast it might just be advantageous to use GLM instead of writing and debugging my own stuff. Another question is, would there be compatibility or speed issues using GLM with Direct3D?
GLM is a math library that tries to be close to OpenGL conventions (ie vec4 instead of float4), it doesn't depends on OpenGL calls as far as I know (it shouldn't have any reason to). Anyway, you'll have to watch out for column-major matrices and right handed coordinate system that GLM uses.
Here's a link I found http://msdn.microsoft.com/en-us/library/windows/desktop/bb204853(v=vs.85).aspx
You can check GLM sources if you're doubting their quality.