For single brightness mode, I like the Elzetta ZFL-M60 which includes a Malkoff M60 as the light engine standard, and comes as a complete light. It can be ordered with a simple on/off twisty tailswitch for around $120 on line. Or if you prefer a clicky, you can order it that way too, for a little more money.
Same basic story with the Malkoff MD2 turnkey without hi/low ring. That will give you one brightness mode, and is around $119. It comes with a Malkoff M61 module standard, and comes as a complete light.
With both of these lights, they can accept all the Malkoff modules, and as previously mentioned by others, there are lower brightness drop-ins available such as M61L, or M61LL, or their "warm tint" counterparts M61WL or M61WLL. The lower output extends the runtimes, and some of the LL versions will run very long times at around 60-100 lumens.
They are "lego-able" so you can use 3-cell or 4-cell battery tubes with the Malkoff lights that will use 123 or 18650 batteries. MD4 takes 2x18650 or 4xCR123 batteries. MD3 takes 3CR123 or 3xRCR123 batteries. MD2 body takes 1x18650 or 2xCR123.
Elzetta does not take 18650, and is restricted to primary CR123 or RCR123 batteries in either 3-cell or 2 cell battery tube options.