Yeah the torch this guy bought also uses CR123s. I know nothing about batteries. What's different about these?
Lithium primaries are nominally 3 volts, usually 2-2.5 under load. They perform well under heavy load, in cold weather, and are short and light. Like coin cells,
do not buy these at any B&M retail store. They range from 1/10 to 1/3 the cost online, and you can even get US-made ones for $1-1.50/each in bulk. If you can justify having 4 or more, it's cheaper to get 8+ shipped to you.
However, alkalines are bad in cold weather (even in the southern US, it gets cold enough outside for them to be a problem), alkalines leak, and alkalines perform very poorly under high current loads. So, many higher-end makers go with Lithiums just to not have to deal with people using alkaline batteries and having problems with them, and dirt cheap ones do it so they can use cheaper/easier circuits.
Many flashlights support rechargeable Lithium Ion type batteries, too (nominally 3.7 volts). It seems that while they won't officially sanction its use, even SF is making a few more models here and there with slightly wider tubes (the + contact is added, a vent, and a protection circuit, then held on with a casing, making it slightly wider in diameter than a primary), and using circuits with a bit higher max voltage. Unprotected cells may have more capacity, but they might go BOOM. Some that don't actually need any protection features, yet also have decent capacity, are finally coming out, though (Google "AW IMR").
If you have alkaline-supporting AA or AAA flashlight, and you either can't keep it going high for long, or go through a decent amount of batteries, you may want to look into getting LSD (low self-discharge) NIMHs (Eneloops being the first and best, but others are good, too). NIMH perform well under heavy loads (AAs can take an amp or more before nearing 1V), can be recharged, and have decent capacity (typically 70-80% of AA Lithiums). Also, unlike traditional rechargables, they lose very little capacity over time, so they don't constantly need to be recharged (<20%/yr). Rayovac Hybrid and Duracell Precharged are common retail brands of these.