Most of those comments are about the Corsa which has a slightly different tuned engine. 75bhp vs 90bhp in the Astra. Its probably the same basic engine though. Problems with the engine managment light with Opels seem quite common across all their engines, both their engines petrol and diesels. Its not always a problem, just the light comes on. But dealers seem unable to fix it. Our old astra had the light come on now and then but it never caused any problems.
Having driven the Astra, 1.3CDTi the lag, hesitation they are talking about, I also noticed but I thought it was simply turbo lag. Was overcome by simply revving a bit more. But then again maybe they are talking about a different problem who knows.
I'd have though the .13CDTI might struggle a bit in heavier estate though.