And you know why the cheap ones malfunction so much? Because part of what you pay for in the expensive models is the quality control and adherence to specifications during the manufacturing. So yeah, it's possible they are built in the same factories but that doesn't mean they're build to the same standard.
I'm all for saving money where I can, but I wouldn't try to save a few dollars on something as dangerous as a battery, which can and do explode/overheat while in your pocket or hand. But I guess that's up to you and your priorities.
its up to you...but i done the test when I have the Samsung galaxy S2 and S3
Mugen vs Anker vs some other brand and from what I see, there is absolutely no difference, if a "sticker" from Mugen justify you paying 1/5 of the price of the phone then go ahead...but its better to educate others so they don't make the same mistake.
P.S all the phone that I used that have removable battery or battery case, I never had one that will "explode" in my hands...