Im not the most up to date on the reef world trends, but I have had a lot of tanks set up in various configurations over the last 18 years as I am more of an old school reefer than most here.
First off, I will say that technique can definitely work for you, no doubt about that as I have set a couple up like that in the past and did well. But I think this is best suited for larger tanks and those that are taller as well. That DSB is gonna need a lot of fauna living in it to work properly. In small tank I have found that Fauna can be quickly depleted or reduced in numbers to the point its no longer effectively working as designed. If that happens your likely to have water quality issues especially the longer you have it set up.
My first jump in to Salt Water was with a 55 gallon tank set up with a DSB. It worked great for a while as I had very little in the way of fish. It was still kind of a cutting edge technique at the time. Corals were becoming easier to keep and came in more colors than doo-doo brown and ho-hum green, lol! High Tech lighting consisted of the new 10K halides and VHO Actinics! Man those were the dinosaur ages!!! Things went well for me with that tank growing Softies and LPS, but when I started doing SPS corals I struggled mightily with Nitrates. Eventually I abandon that technique in favor of a shallow sand bed (@ 3/4-1") and lots of water changes and vacuuming. I have to admit, I did enjoy the plethora of fauna in the sand bed though! Now I am starting to experiment with a BB tank...I guess I am OCD and Lazy too, the older I get these days!
With Nano Tanks...I think a shallow sand bed or BB tank is the way to go and the path of least resistance. These tanks have small volumes of water and it doesnt take much for them to get out of whack water chemistry wise and crash on you. Hopefully others will chime in here and give you better advice on this than I. I havent been doing Nano reefs until the last 8 years or so...so I am still kind of toying around with them a bit.
