Maybe a bit early to chip in here, since I only received it in the morning. But I can give you first impressions, for whatever it's worth.
I've got a 6 wrap Kanthal 28GA build in there, 2.5mm ID, spaced, 0.93 Ohms. Cotton Bacon v2. Wick ports filled but not stuffed, wick holes free. Coil about 1mm away from the bottom air hole. I'm using the 4.5ml tank. Airflow "wide open"... that is as open as it gets with the Berserker, which translates roughly to the 2nd hole on the Ares or 3rd hole on the Siren 2, for reference. 18.5W. Flavour is fantastic!
This is the first build in there, and it seems I was lucky to get it right. I've refilled twice (I deliberately didn't fill it more than about 1/3 so I can practice refilling it - it's got a repuation for leaking, flooding, gurgling etc). No gurgling, flooding, leaking for me - yet. Let's see how it fares over night.
One thing I always do with screw-on top fills is to fill it up, then screw until I feel resistance, turn the whole thing upside down, wait a moment, then screw it tight. Works with most tanks okay, and did work with this one as well.
I was sceptical and am still (I seem to be a bit too lucky so far), and I only bought this tank because FT had it for $27 with MAP code ($44 normal price), which is dirt cheap. I expected it to be too tight of a draw, because it's praised for that by virtually every single reviewer out there, and I prefer a slightly looser MTL draw. But the biggest hole is spot on for me.
I think I've got pretty much all budget MTL RTAs that came out in the last 6 months or so: Siren 2 (22mm version), Ares, Hastur, Merlin MTL, and then some: Doggystyle, Coopervape version of the Skyline. The Berserker might just edging it on the flavor side. Hard to pick a winner.
Sorry about the wall of text. I shall spam you more in a few days to comment on the alleged leaking/flooding issues.
Edit to add: I'm using 70% VG juice.