Here is a thread on the WO61. Post #6,#7, and #8 show a good example of the effects of a Flattener.
No, a Flattener is not neccessary for EAA. The basics for EAA are a telescope (or lens), and a camera. The camera is used to enhance observation, so generally short exposures are used for near real time observation. The images can be stacked by the use of software (such as Sharpcap), or even within the camera hardware as in the case for the analog Revolution Imager camera. Any/All other accessories, while not neccessary, are generally used to improve the experience. There are many approaches to EAA, and it’s always fun to see how people push the limits, even break pre-conceptions of what is capable with modest equipment. You could even use a simple photo tripod, small camera with lens, and stacking just a few short exposures to enhance observation.
The SkyWatcher AZ/GTi offers abilities that while not neccessary for EAA (like GoTo, and WiFi), are features that I enjoy and wanted in a small, lightweight, portable mount. In addition, the ability to use the mount in EQ Mode, along with guiding, will allow me to explore longer exposures. This would be more like conventional astrophotography, and will also benefit from the field Flattener. So while I did purchase, and plan to use the Flattener for EAA, I also got it with longer exposure imaging in mind. Likewise, the guidescope (and guiding) will be neccessary for long eposures, but no so much for EAA (I’ll use it for both).