Difference is mostly in the basic design - vacuum arm is mounted on the cover on the 16 & on the 16.5 arm is on the platform. 16.5 has a reservoir - 16 doesn't. Why they changed it, I'll never know. Probably for marketing reasons-to get the 16 users to upgrade to the latest. Both are indestructable & clean equally as well. Biggest factor is the user's thoroughness using it. Grab it fast- only way to enjoy your LPs is when they're properly cleaned.....
