I've owned my Extender for 3+ years.
I've had no issues with it. I previously owned a Toyota Pre-Runner and 2 Mazda BT50's. In my opinion the build quality is certainly as good as the Mazda, and running costs are around the same.
Mine is the 4-door, auto, i-smart model. It has an incredible spec for the money; 5 years free parts and labour servicing, disc brakes all round, tyre pressure sensors, auto lights, large screen infotainment system, cruise control, loads of legroom in the back, plus more.
I paid less than 800,000 baht for mine.
Would I buy another one?..........Yes.
Go and have a look at one.