Yeah it is definitly a workaround, unfortunately it is the only way to modify the Speed values outside of the material graph.
Just wanted to add a couple of notes here. You will want to set up the MaterialFunction’s details panel similar to the image below. This will expose the function to the Palette so you can use it in any material. I added mine to “DC_Functions” which is where I put my custom functions, but use whichever category you want.
Here is an example of how to use the function. I added in both a CollectionParameter and a VectorParameter to show how both can be used. Since they are 4 channel vectors by default, I mask the R & G channels, but that is not necessary since the function masks the input as well.
So this is the only way currently to modify the speed, I mentioned it to Epic before that it would be nice to have this exposed to the regular Panner node as well, we’ll have to see if that gets added in a future release.
Hope that helps! 