I have one on a 123 body. I also have the tailcap modded. Therefore its a 3 stage light. Its simply awesome, and the levels correspond very closely to my HDS lights (without the minimum super dim setting that the HDS offers).The beam is very white-not on the warm side like my L2Ps. And, in real world use is as bright as my U60 & B42 on high. Can't tell you about the runtime, as I don't EDC it, but use it around the house for up to 1/2 hour a day. Its as bright as the first power up, and on the original primary battery.
I have an L2P on a 123 body, and have been considering buying another L1T/L2T to upgrade the 123 body to. The 3 stage option is really handy. I might add that the 123 body and head assembly is the same length as the L0P, and just slightly thicker.