Hi and welcome to the forum. You will have one switch or button. This will turn the saber on and off plus provide a clash lockup effect. Since your choice is the 2-channel Emerald driver with the v4 Obs. you can manage your flash and pulse effects from your computer. Will still use the same button for the flash lockup and to change the eight sound fonts.
So you need to decide if you are going with the standard black plastic guarded switch or pay a bit more for a silver or black AV switch with or without illumination. You can request a VA as your main blade color and another color as a pulse and even another as a FoC. US will install this on to your saber prior to shipping and then you can change it at home. Just remember that the Emerald driver board is situated higher on the left side of the battery pack and be mindful of the speaker.
For example. I have the same Emerald as you. Main blade red ( BR ) with quicker pulse to dark violet amethyst ( DVA ) and flash of Banes Heart ( BH - magenta pink ). My request to have it sent this way placed in order comments. Should have requested a slower pulse color change but I could modify it.
What saber are you getting ? Don't forget an extra set of Li-Ion batteries and the VP1 charger is well worth the small extra cost.
