I've been running my Nano 2025 for 3 weeks now and thought I would add to this post.
I am absolutely thrilled by the amount and type of flow this pump produces. I run a seahorse tank so I didn't want any narrow strong streams of water in the tank.
ALL the water in my tank is now moving. I have enough flow for corals, but the velocity is still low enough that my seahorses are still happy.
I do find this pump noisy comparted to my other powerheads, and because I do not run a skimmer, do notice it. Given the flow, its a reasonable trade off.
Assembly and installation were dead simple and the design of the holder is a marvel. I can stick this pump anywhere and it stays stuck. The directional adjustment is brilliantly simple.
I spent a day moving the pump around in the tank to get the right flow and it was a shear pleasure. Sooo much easier than a traditional powerhead.
Tunze must be using a German inch though, because I measured the housing at 3". 2.5" would have been wonderfully compact. 3" is quite reasonable and, as you can see from pics others have posted it is a smaller footprint than powerheads.
Overall I am really, really happy with this pump so far. If it holds up like other Tunze products, it will be the best pump I have ever bought.
Fred