I must give a shout out to the vandy vape Berserker mini mostly as I have been using it for a month now and just adore it.
Pro's
No leaking, mine does not leak despite being carried around in my pocket or back pack all day. Also I work in a variety of temperatures so its not even leaking when it gets all but frozen and then taken into an uncomfortably warm room repeatedly. Obviously no tank is meant to leak and does not leak, should be an expectation rather than an exception. However as that is not always the case, it remains a big pro for me.
Vapes great at between 8 and 12 watts depending on if I am using 12 or 20 mg salts, my preference is vg/pg 50%. However I have put plenty of 70/30 through it and it works just not as magical imo. Obviously what you vape it at is going to depend on wicking and most importantly the coil. I have used Vandy vapes pre-made super fine mtl coils and they are great. With that said its so easy to make your own coils for MTL build that basically any fine wire, looped six times is going to give you what you need.
As I do like having pre-made coils around though the fact those are around 3 quid for 10 and easily found is a benefit. There is also a uk based, crazy wire company who make imo better coils from pure/trustworthy wire and those are also super affordable. You get the idea, vitally its easy to coil.
Build is super simple as most mtl tanks tend to be and once you have the hang of wicking it, you could do it in your sleep.
The small size means I can put it atop of a nano device, in my case a Vaparesso Tarot and still have battery for days, even as a heavy user due to the low power vaping. I would feel weird having my baby tank sitting atop a dual 18650 mod but that's just me.
Cons:
Only real complaint I have is that the threading of the tank seems to gouge at the orings slightly, which means they may not last as long as one would like. A month in and I have had no need to change but it still seems like bad design. Could be user error or my bad luck, it has not ruined the device for me but it does need a mention.
Any of the well known, well reviewed mtl tanks you get is going to make you very happy! I mentioned the one I have experience with for obvious reason. The important part for me though, is that as good as pod systems have become a good RTA is going to blow them away. I have had a breeze along with a few other MTL pod/coil devices and nothing has come close. My friends who still smoke will often happily puff away on the Berserker but never cared for my previous kits.