Great info in Hoople and Karl's responses. I put a Dynatec HD1 unit on my '92 Dyna Glide back about '94. I can (and have) go from single to dual fire with a flip of a dip switch. Honestly, the only difference I can tell, is the idle is a little more "lumpy" in single fire mode. I'm running a .530" lift, medium duration cam.
Breeze' experience is probably what you would "hear & feel" in the saddle only IF your engine is "built up". The actual ignition "moment" is quite short and possible electrical "coil saturation" due to doubling the firing rate (having to provide wasted spark) not allowing inductance to build/fall quickly (hysteresis) is likely not detected with Stage I mods below 5,000 RPM. :hii