People that have had them seem to love them on civics (me being one of them).
The way I see it is, D2s are around £450 - you will pay twice as much for a premium brand - £1000 for Tein monoflex.
Performance wise, I'd say most of us wont notice much difference between premium (e.g. tein) and D2 - although how many can say we've tried them back to back. Yes, they haven't the adjustability of premium makes, but the lack of adjustability seems to be down the softer end - if you like it hard then they are great. And TBH, choice of spring rates will have a greater effect on ride than damping adjustability.
In terms of build quality - OK, they are not as well made as Tein etc.. but what I like is that Impulse Performance (the importers) have A1 backup - any leaks, they will replace, quickly!. They have all the re-gassing equipment so if you want your damping uprated (to take stiffer springs) they can do it FoC. They can supply the coilovers with the spring rates you want (Tein are fixed so it's another 160 quid if you want something stiffer). If you're Tein leaks then it's £100 quid plus parts plus a few weeks wait!
I've had D2s on a K20 civic and S14 and I couldnt fault them - the handling of the civic was awesome. However, I did buy some for my Dc5 and the design/build quality was rubbish so I returned them. The ones for the civic however, are a completely different design and IMHO great.
I am currently deciding what to go for - Tein or D2, I don't know why - if I listen to other people (you generally haven't ever used D2s) they say Tein, but then I loved D2s on my civic and I'd rather ut the extra 550 quid towards a Godspeed AP racing brake setup