Cryhavoc, the McR38 was used to fill the head diameter, the 27 would have left gaps around the reflector. In order to fit the depth of the reflector, the inner bulkhead was machined away, and the reflector passes through it to meet the LED which you can see is about as low as possible in the head.
Bernie, the converter does many many things I don't need, but the basic menu is low-med-hi. After you run through those levels, you can access many fancy features such as strobe, hi-lo beacon, blink, heartbeat, wave, and some others which are cool to show off, but don't have much practical use for me. To advance the mode simply cycle the power off-on.
Pictured is a chromed SW01, which IMO looks best, but I also chromed an SW02 which is easier to use with the multifunction. Surprisingly the fat SW01 allows you to cycle through the menu and latch with a one-handed twist after a bit of practice.
What I like about this particular converter is that it always reverts back to the beginning after it is turned off for a couple seconds. Also, you can advance the mode regardless of how long the light is left on - you don't need to start over. These are minor details, but it is the only multifunction converter that I can use and never get lost. I always know where I'm at, where I will go, and where the light will be when I turn it on.
It is the same converter in Arcmania's Digital Tower Module, the last incarnation of the SF turbo head modules which use the Seoul. I believe Mike is soon releasing the Maxlite Extreme 2 which will use the multifunction converter as well to power a Seoul, and be driven off a single AA cell with a 20 mm head instead of the 27 mm used to date. Though I'm not a big fan of multifunction converters, this is the one that I like.