PLA Economy compatible with Ultimaker 3, Ultimaker 3s, Ultimaker 5s?
Of course!
The only difference is the size and weight of the spool which holds the filament. The filament itself is available in 2.85mm (+- 0.1mm).
Instead of using the original spool holder we would recommend using our 3D printed filament duck, https://www.thingiverse.com/thing:1862683
You could also suspend the spool in a self made rig behind the 3D printer.