I used my Taifun BTD clone for 6 months without the PEI chamber reducer, it mattered very little/ none at all...

the Citadel, however, was designed up front with the insert in mind. The main difference is the sound it makes. Flavor is still fantastic and top-tier. I've never had spit-back from it either way. Great rda, and it's time for a new effort from Psyclone.