Looking at the way the Ehiem pump is connected, it’s a downstream design.
My problem with a downstream design is that the sediment that get passed through the filter will ruined the pump shaft. I would reverse the flow in the design to upstream.
I do see this a viable option for smaller tanks. Couple with a paintball Co2 canister size with a regulator will run a small tank for a long time.
Yes, it's downflow, and no, sediment does not mess up the pump. No significant amount of sediment comes through the foam filter. I have an identical (but much large one) running on my 450 gallon system for the last 10 years. Same Eheim pump. Same piece of foam, pretty much same everything.