As far as you are using core feature, I can say that GLM is fairly reliable. It is used for commertial software, the number of users is became large enough for quick bug report and GLM have been used for a varius kind of applications: OpenGL, raytracing, sketelon animation, geometry morphing, image processing, etc.
Is it perfect? No, complete unit tests would be required for this. GLM extensions are still mark as experimental. To be fair again, most of them are quite stable so that I expect to mark them as stable.
GLM is suposed to be easly extendable so that you can create your own features.
Concerning the template errors nightmare, it can happen but it's definelty something I have considered.
Those days, one mistake can bring you hell: type mismatch. 1.0 != 1.0f or size_t != int or char even if all values are zero. GLM and GLSL are strongly typed, because of templates but it matches with glsl spec.
Don't hesitate to report any issue, it makes glm become better and better!
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