wonder what the difference is
The difference is size. The CR123a version is much bigger than the one that takes the garage door remote type battery. Both are marketed as markers.
The earlier (smaller) one had far less confusing flash modes and is IMO the better unit if you require a marker beacon or small light source.
The Lithium (CR123a) version is brighter (much) and is marketed towards waterproofness, with dive marker listed as a particular role.
If you want to use either as tent lighting expect to be squinting a bit, thet're designed to cast light 360 degrees. Both have clear bodies from which the light is relfected out. Neither works well as a torch. Personally I think they're overpriced and have very limited applications.