The bio wheel is a nice idea. But when the spraybar clogs or the rail the sits in gets gunk in it, or the water level Frops, etc, the wheel will stop spinning. When it does, whatever bacteria is on rhe part of the wheel that's not submerged will be dried out and killed. And the wheel only has the surface area of a handful of bio-max to begin with.
The idea of a HOB with wet/dry capabilities is cool, but thus far unsuccessful. if you really want wet/dry function, build a DIY wet/dry sump. Its cheap and relatively easy. You can prrbably build one for the same price as the Emp400 or less, and it will be way more effective. if you want the best HOB on the market, go with the AC110. Remember, canisters don't even use wet/dry filtration (with the exception of a couple of eheim models like the 2227/2229), and just about anyone will tell you to get a canister over an Emp400.
If you're just looking for the best HOB on the market, the choice is clear... Aqua CLEAR. Lol.