I have the 3-cell body and the Hi/Lo clicky switch. Great combo.
If you can tolerate the little bit of extra length for the 3 cells, you can get more run time and also use the M91 XML drop-in from Malkoff. The M91 won't work on 2 cells unless they are 16340 li-ion, and that's a very short run time with those.
Also, regarding the "custom" p60 drop-ins, you need to be aware that the Elzetta is internally shaped to accept only the Malkoff drop-ins, for best thermal performance and shock durability.
Other drop-ins might not fit, and certainly won't be a perfect fit for thermal performance.
Thankfully, it's hard to beat the Malkoff drop-ins, so having a perfect fit for them might not be considered a limitation.
Also, the Elzetta bodies are not bored for 18xxx size li-ion batteries, and are actually made to use primary CR123, for reasons of safety in high-recoil weaponlight applications.
I have heard that they can be bored for wider cells, but I have not done that with mine.
And lastly, since all the Elzetta parts are "lego-able", you can buy a 2-cell body any time you want, and make your 3-cell into a 2-cell by just changing body tubes.