I actually saw these in the catalogue for last week and a whole bunch of other things! Unfortunately our Aldi didn't have any of these things I wanted to look at so can't really help you much.  Do you know the ingredients in them?  All the carbs would be from the flour, being shortbread they use plain flour and sometime rice flour as well.  It infact may be no sugar, but the real question is what other type of sugar substitute did they put in there instead to keep it sweet (my guess would be some sort of artifical sweetner).  Have a closer look at the ingredients, if the substitute sweet is ok then I think it's fine for a treat.