I think it's probably more effective on cars with shorter gearing since they are the ones that run less efficiently at steady state. I haven't ever tried it since I don't have my own car, and my mom would freak out if I were putting the car in neutral on the highway, but I would be a little scared to do it with other cars around because I feel like a lot of drivers use either cruise control or just go as fast as possible as long as it's under 80mph
. Making the pulse intervals short would require more work and possibly more drivetrain wear, making the pulse intervals longer would confuse other drivers and possibly create a dangerous situation.
The theoretical gains possible are really attractive though, I will probably end up trying it someday.