Like the inner diameter is too small? Kevin told me he could provide the extension tube for the 18650. Maybe he was just confused. You can see, the ones that take the 16340's, the tail cap is very close to the key-lock. Some you can see they are a little longer by roughly 2 inches or so. Can you confirm if an 18650 fits in the HL host, diameter wise? That would be good to know for future reference.
LaserBTBs Handheld pointers have a duty cycle in seconds, portable lasers are in minutes. For alignment purposes I've actually kept my HL520 running over 20 minutes at a time with no apparent issues with the laser. It gets warm up to a certain level, then it stays there. On the other hand, I've burnt out pens one by leaving it on past 5 minutes.