beware of scammer and flipper

E-Cig Wikipedia

There are three main classes of e-cigarette: mini, mid-size and APV.
Each has its advantages and disadvantages, which are briefly outlined here.
1. Minis
A mini or regular-size ecigarette is usually the newcomer's first choice, because these models look and feel similar to a cigarette. A mini is a good way to try out the system at minimum cost.
Although they have a million brand names, they are all in fact models with a recognised series number that distinguishes them from others by their thread type and fit. In other words a 'Whizzocig' will turn out to be a KR808 or whatever. If you know the model series then you can mix 'n match parts from other vendors since they will almost certainly fit - there are no proprietary models despite what the makers may claim; all have a model number.
These are called 1st-generation models as they were the first to be invented. Originally all these models used the 3-piece system, with a battery-atomizer-cartridge. Now about 95% use the 2-piece system of battery-cartomizer. A cartomizer combines the atomizer and liquid reservoir in one unit.
Polls tell us that about 8% of forum members continue to use these models frequently, although many more keep one as a back-up or loan model. The batteries range from 125mAh size up to about 280mAh.
A mini is a good choice for discreet use, and as an initiation to the ecig concept. If a model is chosen that looks exactly like a cigarette - white with a red LED tip - then it can be used where you would smoke a cigarette; but don't try using it indoors because people will assume you are smoking and no amount of explanation will fix it as there is bound to be confusion or resentment from some. Instead, get a black one with a blue or green tip, it will create less problems because it is harder to confuse with a tobacco cigarette.
The models include the 510, 901, M401 and KR808 (often shortened to KR8).

Advantages:
Looks and feels like a cigarette
Small and discreet
Auto and manual models
Cheapest way to get started
Parts can be re-used if you know the model type
Ideal for light smokers or occasional smokers

Disadvantages:
Batteries do not last long in use - from 45 minutes to 2 hours for some users
The other two physically larger classes have better performance
Will probably not provide sufficient performance for heavy smokers or full-flavor smokers
The auto batteries can be destroyed by liquid leaking due to over-enthusiastic refilling

2. Mid-size
The mid-size ecig is the #1 rated model type because it suits most vapers, either as the main device or the main back-up. The common names are eGo, Riva, Tornado, kGo and others.
These 2nd-generation models have a much larger battery size of at least 650mAh. This has three important results:
The batteries last longer in use;
They produce more vapor than a mini;
They can use a much wider range of heads, including - crucially - the LR type, which produce more vapor. All kinds of tanks and other exotic heads can be used (the liquid reservoir and mouthpiece arrangements).
Most of these models are based on the 510 range although some use the KR8 thread.
This is the type upon which all ecig measurements and values should be based: it is the average in all respects - probably about three-quarters of forum members either use one as their main device or keep one as a back-up.

Advantages:
Not too expensive to get started - maybe 50% more than a mini
The 510 series threading most used has a huge range of heads
The small, 650mAh battery is reasonably small for those who want it discreet
Looks and feels like a cigar, so it's not too big
Double the performance of any mini - double the vapor
Batteries last well in use, the bigger batteries around 1,000mAh can last up to 8 hours for some vapers
Should provide sufficient performance for most smokers, especially newcomers
The #1 rated type of ecig for good reason - suits more users than any other type

Disadvantages:
Almost exclusively these are manual ecigs - a disadvantage to newcomers although an advantage to experienced users
Slightly more expensive to start out with
Ultimate performance is not possible as the battery power/voltage is not sufficient

3. APVs
Advanced personal vaporizers (aka 'mods') are the logical progression and development of the ecig concept for those who want ultimate performance. They can be defined simply as any model that employs user-replaceable generic batteries and/or has a function not normally available in a mini or mid-size e-cigarette. There are two main classes of APV: the tubular shaped tubemods and the box shaped boxmods, and three sub-types: mechanical, basic electrical or electronic.
hey do not normally suit newcomers because they are too big, or weird-looking, or too fiddly to use; plus all are manual-switch models. These are 2nd-gen or 3rd-generation devices. Almost all have a hugely extended battery life over the minis, and they mostly use generic 3.7 volt lithium rechargeables that can be bought from many sources. An APV will normally look like a fat tube reminiscent of a flashlight with a mouthpiece (a tubemod), or a box the size of a pack of cigarettes with a mouthpiece (a boxmod).
the big advantage is the performance that large batteries deliver, plus the advanced functions and features that are variously available according to the individual model: integral liquid feed, digital readout, variable voltage, full electronic control, solid metal construction, or attractive wooden construction with inlays, and so on.
We suggest that an APV is not purchased as the first model by a newcomer, but instead a mid-size (or mini) is first used to gain familiarity with all the many aspects of vaping. This also has the advantage that there will be a better appreciation of the many issues if choosing an APV later on.

Advantages:
Massive performance gains: three times or more than any mini - treble the vapor volume
Extended battery life
Solid construction
Some of the base units may last a lifetime
The advanced functions are extremely useful
Batteries last a very long time in use, the average is 8 hours although some can last for days
Will provide sufficient performance for any smoker

Disadvantages:
Expensive to set up with - some base units are over $200, though there are many far cheaper
These are all manual models - a disadvantage to newcomers although an advantage to experienced users
Some care with battery charging is needed, as large lithium ion cells need treating with respect