Better get one mod per attachment if you want to make TC mode work, that's what they recommend in the e-cig world. Not all 510 are created equal though, some are better, but those from Joyetech/Wismec/Eleaf are notoriously bad. I experienced it first-hand myself: my brand new evic Primo mini was used solely with the iHeat but just the fact of unscrewing it a few times to show to other people how it was built was enough to ruin it.
Now it's almost unusable, just blowing on the attachment makes the resistance change, and without a stable resistance reading you can't get TC work without huge variations in temperature (I'm talking over 40°C variations here, so either you combust or you get no vapor depending on which direction it went wrong) It might also be related to the 510 base that Alan selected as it feels a bit too wobbly to me.
I went back to my evic VTC mini and it's kinda ok. Yet I still have to double check the resistance everytime I power it on as it can still vary. Plus I still have that weird unexplainable bug that developed when I used it with the Project and other custom RDAs.
I hope Ryan spared no expense when he selected his 510 base source, as it can make a huge difference for long term reliability.