I emailed Ecover regarding the preservative used in their delicates wash, they told me they are looking for alternatives to it but they did say that the concentration is exceptionally low (0.02%) and that as it gets rinsed away it shouldnt cause too much of a problem. Personally, i do use the delicates wash but because I rarely wash woollens, I dont come into contact with the detergents preservative (just my opinion).
I've used the concentrated non bio Ecozone liquid and their fabric softener in conjunction with the Oxygen whitener for towels and whites, I found them to be satisfactory for my needs but Ecover I felt was more convenient as I didnt have to go out of my way to buy it and I preferred the scent of the Ecover, I did find that the Ecozone liquid wasnt very sudsy but it seemed to be ok...