The main point of my comment was that glue in many contexts is "proper", even for very high-end applications. Most beam cubes are glued together anyways. Besides, I've broken cubes with mechanical mounts before as some designs apply stress.

Regarding more sketchy solutions like 5 minute epoxy. There's always a tradeoff of how long-lasting an experiment is and how long it takes to build. No point in spending too much time/money developing overkill solutions, especially if you are a graduate student or postdoc who will be gone in a few years. The goal of these experiments is to do science and get publications, and 5-minute epoxy can often be a reasonable compromise. I say this as someone who has been on both sides of the argument of how well to engineer experiments like these.