Absence of info about the bin and Vf (especially) are quite inconvenient.
For my own planned mod (3 x Nimh AAs Direct Drive), the nominal voltage is around 3.6v. If I get a K or L Vf bin, it won't really be bright. I'm hoping for a J bin perhaps.
Surefire LED 2 cell or more lights need not worry about Vf bins that much if they are using a "Downboy" type convertor.
But for the e1e + LED head, I imagine the Vf is important? The single Li-on happens to fall at 3.7v nominal voltage and if the convertor was a step down but the K2 was 3.99v, it's not gonna work. Or if it was a step-up and the K2 was 3.42v Vf, it wouldn't work either.
But I guess SF convertors are the 'smart' type that auto-detect the voltage difference and adjusts accordingly.
P/S I hope I'm making sense. I'm not even sure if I have my facts right. Haha...