The difference boils down to about 25$ in cost, and about 75$ difference in the quality especially the electronics. www.balsapr.com
sell the GWS for 160-170$ RTF with low or no shipping. So there is no savings going cheap.
It's said the #4 is a Sabre clone. There is enough difference from the MDF (GWS Dragonfly) and the HB (century hummingbird), that I believe it. having never had a sabre in my hands. IE the swash is a mirror image, the balls/links are slightly different sizes.
My understanding is Feda made most of these (or atleast the parts)at one time and manufacturers went their seperate ways and made changes along the way. Most notably with the MDF they added a electronics box. The MDF and HBv2 (not to be confused with the Esky Hbee FP v2) share many subassembly parts While generally as a whole they all share assemblies, as in you can interchange the entire head. The Walkera uses proprietary electronics so you can't easily upgrade to a better transmitter in preperation for the next level of heli. The others use negative shift and when you start thinking about getting a better heli you can buy a real transmitter and continue until the budget recovers. This gives you a good chance to learn the radio with a simple to setup heli you already know.
General consenses of previous owners of Walkera products is, they would never buy another, and wish they had never bought it in the 1st place (though there are exceptions). While most are happy with the Hbee FP v2, HBv2, and MDF. These are generally beginner helis and as such the reviewers have little to gauge against other than their expectations at the time of purchase which may leave them dissatisfied even with the better helis, which is understandable. IE they find it requires a certain level of skill to fly and think it sucks because it didn't leap out of the box and hover hands off on opening the package. Or tip it over on the first attempt and watch it do the headless chicken routine and are upset because the Xn1 board burned up on the first flight "never even got off the ground".
I've owned the GWS, Century, and Esky, FPs and find them all to be on par with each other in quality, flyability, and crashability. It truely is a dodge, chevy, ford thing with them IMO. I also bought a basket case Walkera #4 and never bothered to put it to rights as it seemed a waist of my time, and infact gave the parts away. Note I had a very good baseline of what to expect and wouldn't use the electronics which left me with putting good quality electronics in a cheap inferrior heli, an option I chose not to exercise.
Hmmm, that may have been more than was needed.