I used the Mothers Speed Clay 2.0 but I like traditional clay better. With traditional clay, you can see the contaminants that the clay is pulling off of the paint and it gave me more confidence that it was doing its job.
That being said, I found that the Speed Clay 2.0 item works well to clean windshield of baked on bug residue and tree sap that don't want to come off with glass cleaner and paper towels or MF towels right away. I first clean the glass with my favorite glass cleaner and paper towels to get most of the dirt, bugs and road film off, then apply a generous amount of glass cleaner and use the Mothers Speed Clay 2.0 to deep clean the glass and then finish up with more cleaner and an MF towel.
At least it didn't end up in a box in my garage with all kinds of other car care items that I tried and never used again.