Ohh big question. I EDC a TW4. I think on one cell the KL4 is direct drive. Do a search for "TW4" and you will find TONS of info. Nascar did some awesome graphs etc.
In my opinion, it blows the LS series away. It was such a hot seller that SF asked Dan to remove it from his site.
You could probably get $20 for the Z52 tailcap from the E1e. The bezel might be harder to sell because there are a lot of them floating around due to people using the KL1/KL4 on the E series lights.
I much prefer the L4 with Pilas, but when the rechargeable 123s come out I'm hoping that the TW4 will perform better than it does with 1x123.
GarageBoy,
That has been my experience though it seems to be brighter for quite some time and then starts downhill from there. I was not aware that there were some KL4 heads that would not work in this configuration. Interesting. Mine works great. I highly recommend it.
Hmm.. if what the TW4 needs is a little more juice, then these might help. I'm looking forward to when the reviews come in, the rechargeable 123s look like real gems.