I snagged a Fornuftig at a local Ikea sale event for the same price as an Uppatvind with the intention of using it as positive air intake for my networking rack (reduce dust buildup from within the rack).
The vent of the Fornuftig, however, wasn't suitable for the rack's 120mm opening because its much wider, and is angled 45 degrees upwards. Granted, this probably isn't the intention of the Ikea designers when they created these air purifiers, but that's where 3D printing shines doesn't it!
I've designed a 220m-wide (max width my printer can print) vent redirect that forces the air to vent directly back of the Fornuftig, funnelled into a 120mm-wide opening as that's as wide as my rack's ventilation fan grilles are. For my use-case, I simply laid the Fornuftig on top of the rack with the vent facing down into the grilles. The picture will probably explain it better!
Some slight 2mm gap because of eyeballing measurements with a ruler, but could probably fit better if you scaled this up by some 5%.
Some tabs are included to stick adhesive tape on the top (where the speed adjustment knob is) surface to keep the vent from sliding away at higher fan speeds.
The author marked this model as their own original creation.