This is all relative to light pollution. If your under truly dark sky 5mw is plenty for an astro pointer.
In the city it may not be enough, Although its a bit pointless doing astronomy in light polluted areas though.
<--------Is also an astronomer
I just used J/B weld. Its what I had "laying around" Yes they both turned out well. I used a razor and scotch bright to remove metal from inside the pen so the cap could freely turn which is what took the longest to do. The red pen's lense really didnt want to un-screw it was a total pita.