I like the flat top so much better. "no knurling" ALSO NO VENT HOLES. So, just to be safe... safety fuse your mech. I was dripping last night on my flat top gold n chrome, with my new dual coil rba. My poor 18350 efest just did not last to long. But this device is AWESOME!!!!! I am still not going to part with my sig's. I am hoping an SG-2 adapter comes out soon for this. It should not be far away now.I really like it - it's a big improvement over the original top cap. I have to retract the bit about the diameter being a perfect match, though. The RSST is a little less than a mm wider, the AGAT+ less than that. So not quite the "hybrid effect," but very sleek and streamlined. And no knurling!