i have had bad experience with those ones. I have never torn up the clutch type but have torn out 3 or the cone type.
1.was in a stock 318 barracuda. the pin in the middle came out and tore up the ring and pinion gears.
2.was in a 360 dart same thing happened
3. was in another 318 car.

they were all 4 speeds and so that was hard on them but only the 360 car had very much power, high 12's in quarter. i will never run another one of those units. trashed 3 sets of gears with them. i have never broken the clutch type and i have one behind my 440 dart.