OK, here are my thoughts and experiences of the Cthulhu Hastur MTL RTA, Siren 2 GTA MTL and Berserker MTL RTA.
In an attempt to offer my personal experiences with various MTL devices in a like manner, I have coiled with 28g Kanthal, 2.5mm ID, 8 wrap which comes in at about 1.5ohm, and then wicked with Muji organic cotton. All this just to have a comparable baseline from which to compare apples with apples.
Of course, all of this is just my personal opinion, and your experience may well be different.
Any errors are all my fault 
Cthulhu Hastur MTL RTA
This is a 24mm MTL RTA with 3.5ml juice capacity, which comes with 5 air flow restrictors, a spare frosted glass, and the usual O-rings and screws.
The build deck is in the middle of the Atty (RDTA style), and accommodates a single coil, with the added advantage of accepting either a clockwise or counter clockwise wrapped coil. The coil posts are side slotted which make the insertion of the coil legs easy, as does the slightly recessed section into which the screws trap the legs. A nice touch which to me made the process really simple and hassle free.
Wicking is easy, just fill the channel with the same amount of cotton that snugly fits through the coil, dangle the wick into the chamber RDTA style, wet up your wicks, assemble and fill through the top section, which is a bayonet type cap release making filling really easy, however there is not stop detent so it can rotate 360 degrees, so caution when fitting is needed. The bayonet top cap stops the build-up of pressure in screw on type top caps, that could force liquid up to the coils causing flooding, which I have not had with this Atty
Great airflow, and easily adjustable, with the included restrictors and the AFC on the base you will have to try different setups till you find your perfect air flow.
I found the AFC very tight and difficult to adjust on the mod, even with some lubrication, but once set (off tank), the AFC stays in place.
I was not able to work on the deck with juice in the tank, which is a negative to me.
The drip tip is not comfortable to use, and I have replaced it with an aftermarket one.
Overall, a very flavourful vape that has great airflow and is easy to build, and I have had no leaking, flooding or gurgling at all.
Tops for airflow.
Digiflavor Siren 2 GTA MTL
A 22mm MTL RTA with 2ml juice capacity, which is a bit sparse for daily use. Comes with the usual accessories, spare glass and a couple of pre-made coils.
The build deck is in the middle of the tank with trailing wicks, RDTA style, along the same lines as the Hastur.
The two posts accept a single coil with top slotted channels, so dropping a coil in is really easy, and then tightened with screws from the side of the posts.
Wicking is again just like a RDTA, snugly fit wick through the coil and trail the ends down into the tank beneath the deck, making sure the cotton is not trapped in the threads, but ensuring the juice channels are just filled, which obviates any flooding.
Top filling via a bayonet style top cap makes this tank very easy to fill, and as this one has a stop detente inside, unlike the Hastur, there is no chance of turning it too far, and the top cap popping off. Again the bayonet style filler obviates flooding of the coil.
The airflow is controlled by an AFC ring on the base which gives you loads of options, from holes 1-5 or any combination of those. If you want something else the opposite side of the AFC has a single hole that you can line up with any of the holes noted above individually. So the options are really great. The airflow hits the coil from underneath via 3 small hols spread across the length of the coil, which really enhances the flavour.
Overall a very easy tank to work with, that has truly great flavour, with an absolutely amazing deck to build on.
With the thicker O-ring attaching the glass to the base, I found I could work on the base with the tank section still containing juice, a plus in my eyes.
I have had no gurgling, flooding or leaking.
I personally don’t like the drip tip, it is not comfortable on the lips, and I feel that the added little bit on the top could form a germ trap where it joins the main body of the drip tip.
The juice capacity is too small at 2ml, and you would have to go for the Siren 2 24mm to get more capacity.
Tops for build-ability.
Vandy Vape Berserker MTL RTA
A 24mm MTL RTA with the option to have either a 2ml or 4.5ml capacity with the included tank extender sections of glass and chimney. Come with the usual bag of accessories, the tank extenders and a spare drip tip.
A bottom build deck section which is easy to build on, just unscrew the screws and drop the coil in and tighten, no issues were found with thinner wire that I tried. Wicking is dead easy, enough cotton to be snug in the coil, and cut the wick just long enough to touch the bottom of the well, being careful not to block the juice flow holes in the bottom of the well, and fluff it to fill side to side of the well, wet the wick and assemble.
Now here is where I have had some flooding, the top cap is screw on, which seems to create pressure on the juice, forcing it up to the coil. Some people advise to close the airflow, start screwing the top cap on, just a thread or so, then invert the tank and complete screwing the top cap on then open the airflow. Personally, I just don’t fill it to the top, and so far, I have not had further issues.
Note that I only had the flooding issue with the 4.5ml tank extender on, in 2ml format I have had no flooding. Just be aware though.
The airflow enters through a single round hole under the coil, which concentrates the airflow onto the bottom of the coil. The AFC ring has multiple holes, accessed through a single teardrop shaped opening. I have found the 2nd largest hole is best for me.
I have found the AFC ring to be very loose and easy to move inadvertently.
No leaking issues were apparent.
Be aware that if you want to completely disassemble the tank, the screw in the top of the Atty under the top came, loosens counter clockwise, and there is a tool in the kit to use for this purpose.
Overall my experience with this Atty has been very satisfying, the build deck is incredibly easy to work on, even with juice in the tank, thanks to the wide O-ring on the base.
The flavour is outstanding.
Tops for flavour
I trust this is of some assistance to folk looking at these tanks.
May the Fog be with you.
