The popularity of mechanical mods is that they can power self-built coils of less than 1.o ohm. I'm not clear myself why this is so special, but I use an RBA on a variable voltage mod, a Provari. The reason that the VV mods can't effectively power a coil of less than 1.0 ohm is for built-in safety reasons by the processors they use. A VV mod will refuse to power a coil of less than 1.0 ohm. I am using a 2.0 ohm coil I built (I prefer the higher ohm rating because I like a cooler, smoother vape), which can be used effectively on both my Provari and my mechanical Silver Bullet mod.
Most experienced vapors using RBA's recommend using a multimeter to test for the ohm rating of your coils. I bought a $30 multimeter specifically to aid me to build my first coil. What I didn't realize was my Provari can read the ohm with its built-in ohm meter, and can find shorts that I am unable to see by giving me an error code on the LED screen. Also, a variable voltage mod can oxidize the coil before use by doing incremental pulses of power that you can't do with a strictly-mechanical mod. I have yet to even open the box on my multimeter.
I set my AGA up to vape equally well on both the Silver Bullet and the Provari. The vaping experience is far superior on the Provari.