Flat coils are better than barrel coils. There is a simple reason for this:
Many will remember that especially in the early days of enails, most cheap quartz enails were shit because the floor of the dish would just pool up with liquid oil that takes forever to boil or didn't ever fully vaporize!
This was a combined result of the inefficiency of a barrel coil (where the heat is being applied to the sides of the dish, not the floor where your dab is going!) and the fact that the floor of the dish in these shitty cheap quartz nails was below the sides of the dish where the barrel coil makes contact with the nail. Moreover, heat rises. This means that any conduction of heat from the sides of the dish to the floor of the dish is inefficient (especially with quartz!).
Still, anyone who has used a barrel coil vs flat coil for a ceramic nail knows that barrel coils are ineffective by comparison, requiring a considerably longer heatup time. I'm basing this off my experience of the domeless.com nails, I still use their 20mm barrel adapter screwed into my dab table as a stand for my universal 2.0 carb cap, it works perfectly for this - which is fortunate as it sucked for heating my domeless.com ceramic nail lol. Ceramic is more conductive than quartz, yet barrel vs flat coil is still a significant factor!
I should remind all who are concerned about uneven distribution from the flat heater coil to the floor of the dish due to the gaps in-between the wound coil that d-nail have titanium washers to mitigate this issue. The ti washer goes on top of the flat heater coil and below the halo to even out distribution of heat across the dish. These washers come standard with the 1.4 base and first appeared with the Sapphire halo
I have used this for quite some time now and cannot go back to not using any of my halos without the ti washer! It requires a minimal extra bit of heat, probably add 20-50 degrees f to the temp with this one attached.
Finally, the sapphire insert, when used the way it was intended to be used certainly leads to convection heating! You are supposed to put the dab on the sapphire insert before it is on the nail and hot. Then you place the loaded sapphire insert on top of the ti washer with a pair of tweezers and then immediately cap and inhale air, which is heated and vortexes around the load causing it to boil. The sapphire inserts also incorporate the wik technology and unless you overload the insert, you should get no dripping onto the SiC - I never do!
Get a pair of tweezers if you use a sapphire insert with the halos people! If you are just using the insert as a conduction surface, you are much better off putting it into the infiniti large dish (or better still get the other sapphire insert with a match 1.x d-nail dish, which will give you a bigger sapphire surface to dab on).