The only difference to be concerned about between an IDSI and steermatic is the transmission. While it is different, the most complain iv read on these forums is that 'if wrong gear oil (ATF) is poured transmission ka khuda hafiz'. I always think why would someone, for example, would put gear oil in place of engine oil? This is utter negligence, so I would rule that out and if unluckily the car has been through it then dont buy that crappy car. If someone couldnt take care of this small task, you would be able to see his/her behavior with car all through the body, interior and over all feel of the car.
Launching the car from halt has somewhat slow response but other than that, it performs very well (considering I do not use it as a race car). It can surprise you with the punch and you love it at times. The odometer is a great add on. Yes do ensure there was no CNG in any CVT vehicle you buy. The drive is very smooth however bumpy as compared to IDSI (or much stiff as compared to your GLI).
It is a matter of choice, I bought mine 2 years ago because pros seemed to be greater than cons there. Aur jo zada bura naam mila hua hai steermatic ko wo general statements say mila hua hai (dont forget status of automatic cars 10 years ago).