I am no sound expert but I think they sound great.
Both seem to be a little higher pitch than other ones out there. . The Eng sound seems like there a little too much high pitch static noise, which in my opinion, makes it sound dirtier than the others. Maybe give it a little more on the low end to balance it out. Forgive my use of terms or lack thereof I no nothing about sound and EQ. I like that the Start has a sorter duration.
I'm gonna go fly around with them some more!