Very good question !! I think depends on how each driver use and also think.. hehehe
I just did a quick google as reference.. it is about 1.2liter fuel used per hour during idle. If 1 month the idle off for 1 hour total, we saved 1.2L.. that is RM2.46 (RM2.05 * 1.2) saving on fuel.
so 2 years RM2.46 x 24 mths, that is RM59.04 saved.
If don't use eco-idle, et's say the battery life is 3 years, then no fuel saving on idle. Our battery costs about RM300 for eco-idle.
Let's say we put 6 years owning the Alza:
1. with Eco-idle:
a. 6 years fuel saving total RM177.12.
b. changing 3 times battery, hence spending RM900.
c. RM900 - RM177.12 = RM722.88.
2. without eco-idle:
a. 6 years fuel saving total = RM0
b. changing 2 times battery, hence spending RM600
c. RM600 - RM0 = RM600
With the above 2 scenarios over 6 years, then without eco-idle is better. If the price of petrol up, then result will be different.
Just my view and may not be the right one to look at. Please do give your view too as I dont know if my way of view is correct. just something to 'korek' our heads.
If calculate purely on Fuel price, eco idle is to no benefit at all because Malaysia fuel price is too cheap. But maybe soon this will all change with no more subsidy.
For those who use eco idle, a pat on the back for being environmental friendly.
Another thing is that with eco idle, maybe you slightly reduce engine wear and tear as well, but it will not reflect on your service cost as service is by mileage.