I think that's the only difference, as far as I can tell from the specs. The TK11 can use both CR123's or a lithium ion rechargeable. But, if you can get CR123's from work, the TK10 is an excellent choice.

Rechargeable lithium ion-powered lights, obviously, have the advantage of being...well...rechargeable, but they also have the nasty habit of suddenly shutting off when the battery voltage gets too low and the cell's protection circuit switches off to prevent battery damage. That would be one difference between using your old NiCd-powered lights and today's lithium ion-powered rechargeable lights. At least with CR123's, the light will dim first so you have some warning while still having usable light for a fairly significant length of time.