The only difference between the EC2 and EC1 models are the size and weight, the EC1 is meant for a larger hand than the EC2.
Difference between EC-A and EC-B
The EC-B is a revision on the EC-A, there are two primary differences, the upgraded the sensor from the ADNS 3310 to a flawless PMW3360 and they changed the coating to a slipperier plastic on the B version. In general I'd recommend getting the B verison, having a flawed sensor in 2019 is unacceptable.
Side-by-Side Comparison
| Mouse name | Zowie EC2 | Zowie EC1 |
|---|---|---|
| Picture |  read reviewCheck Price on Amazon | read review Check Price on Amazon |
| Length | 12cm | 12.8cm |
| Width | 6.1cm | 6.4cm |
| Height | 4cm | 4.3cm |
| Weight | 93g | 97g |
| Buttons | 2 Primary Buttons 1 Middle Scroll Button 1 DPI Button 2 Side buttons | 2 Primary Buttons 1 Middle Scroll Button 1 DPI Button 2 Side buttons |
| Sensor | Pixart PMW3360 | Pixart PMW3360 |
| Shape | Ergonomic | Ergonomic |
| Cable/Wireless | Soft rubber cable | Soft rubber cable |
| Battery Life | N/A | N/A |
| Software | No software: DPI settings are preprogrammed Step 1: 400 DPI Step 2: 800 DPI Step 3: 1600 DPI Step 4: 3200 DPI | No software: DPI settings are preprogrammed Step 1: 400 DPI Step 2: 800 DPI Step 3: 1600 DPI Step 4: 3200 DPI |
| Warranty | Unknown length | Unknown length |
| Pros | Comfortable super popular shape Flexible rubber cord Flawless sensor | Comfortable super popular shape Flexible rubber cord Flawless sensor |
| Cons | Loud scroll wheel Issues with accidental clicks | Loud scroll wheel Issues with accidental clicks |