Very well stated and I agree with this from start to finish. Love the PT 2's but you must keep them topped off. Also easy to rebuild the heads.First of all, forget the Protank I (both regular and mini). They are officially discontinued by the manufacturer. Both versions had some issues with the "glue" breaking down and causing leaks.
The Mini Protank 3 is the newest iteration of the protank which uses a dual coil design. This makes the "3" coils incompatible with anything other than the "3". The dual coils are designed primarily for high voltage/wattage vaping and since I'm currently not familiar with everything that entails, I'll leave the "3" to those who have more knowledge in that area.
Now we're down to the Protank 2, Protank 2 Mini (rev 1) and the Protank 2 Mini (Rev 2).
The Protank 2 is going to give you higher volume (3ml vs 1.5ml) and is 510 threaded. It has a removable drip tip so If you don't like the metal drip tip that comes with it, you can use any other 510 drip tip. One complaint from some Protank 2 owners is that you have to keep them topped off. As the liquid level lowers, the pressure on top of the fluid due to the air pocket on top of the tank increases and can cause gurgling or flooding. This may especially be true with high PG mixed juices since PG is thinner than VG. While designed for 510 devices, it does have a "beauty ring" that can be threaded over your Ego Threaded device to make it look "better" on an Ego connector.
The Protank 2 Mini (rev 1) is a static tip mini with 1.5ml volume. It is designed for Ego style batteries. You must have Ego threads on your battery or mod to use this device. Due to it's smaller size, it does not appear to have the gurgling or flooding issues that the Protank 2's have. The low capacity is going to be a turn off to some, especially if you don't like filling. Filling the tank is not difficult, but there is not a lot of room between the center air tube and the side of the tank, so you do need to take care to avoid putting juice down the center air hole.
The Protank Mini 2 (rev 2) is exactly the same as the rev 2 with the addition of a removable drip tip. You can the use any 510 drip tip on this unit. It is more expensive then the rev 1. If you like the Kanger drip tips, then it makes sense to get the rev 1 as it is cheaper and has less parts to worry about.
The primary advantage of all these tanks is the glass tank. While more fragile than plastic tanks they will not crack or melt when filled with "tank buster" style juices. Also many prefer the "pure taste" you get from them as some (myself included) can taste plastic after taste from a plastic tank.
The other advantage of the 2 and 3 is the glueless construction. This makes the unit EXTREMELY easy to turn around. You can disassemble clean and dry everything in minutes. I was sampling some Boba's in one of my mini's and wanted to switch back to apple. It took less than 5 minutes to clean, dry, dry burn and refill with apple.