LiMn li-ion cells are a new breed of safe chemistry cell, available commercially as loose cells only in 16340 (RCR123) size from AW, but coming soon in 18650 size, with 18650 and 26670 sizes already available to li-ion powered tool manufactures. (they can be torn down to get at the cells, which many of us have done) This cell chemistry is similar to LiCo in that it shares the same charging requirements and has the same nominal voltage rating of 3.7V. The similarities end there. I would consider these cells to be a notch safer than the LiCo cells based purely on chemistry, as they can not generate their own oxygen during an out-gassing and therefor are incapable of accelerating their own burn in an oxygen deprived environment. (regular lithium CR123s and LiCo chemistry both share this trait of fueling their own fire when something does go wrong, with the potential to become a full blown metal fire). LiMn chemistry cells are good for responsible adult users who know to shut the light off before the battery is over-discharged, as over-discharge will reduce the cycle life of these cells. While this cell chemistry is safer, I would not consider it to be an ideal option for use in a flashlight that is given to a child to play with for fear that the cells may be ruined if the flashlight is left "on" and unattended to completely deplete the cells. Energy density on LiMn cells is about 30% less than LiCo cells, however, in the smaller RCR123 size, since they do not have a PCB consuming a large piece of real-estate (as compared with the overall size of the cell) these cells actually come surprisingly closer to the capacity of the protected RCR123 LiCo cells than do the larger LiMn cells when compared against equivalent size LiCo cells.
LiFeP04 li-ion cells are also a relatively new breed of safe chemistry cell. Commercially they are popping up in many sizes, with RCR123s being the most popular. These are a very safe cell, but suffer from the problem of not being nearly as tolerant to over-discharge as a NIMH cell would be. Since these are "safe chemistry" cells, they, Like LiMn cells, are not sold with PCB circuits to prevent over-discharge. They really do require the user to actively participate in the prevention of over-discharge to prolong the cycle life of the cells, just like the LiMn cells. I would be perfectly comfortable handing a child a light with these cells in it as far as safety is concerned, but the issue of whether or not the cells would survive the attempts to keep the light on long after the battery has gone dead is another issue all-together. As for energy density, combine these cells lower nominal voltage rating (3.2V) with roughly HALF the AH storage as compared with LiCo cells, and these have only about 1/3rd (give or take) the energy density as compared with CR123 primaries or LiCo cells.
It seems that the LiMn cells have slightly higher energy density than LiFePo4 and do not evolve o2 from the oxide chemistry of the Cobalt and others, they do not feed their own destruction.
