I will compare my 3021 series converters. One is NLU and other is LU, there will be very little performance differences. The NLU is slightly lighter and fluid has an easier path thru the converter. My NLU runs on 3 bearings which makes it stronger and is better for use with a transbrake. It can be slightly more efficient over a LU. The disadvantage is the NLU creates heat all the time and will run a little more RPM at cruise and light acceleration. The lock-up has advantages especially if the car is highway driven, fuel economy is better and the converter creates no heat in lock-up allowing the longevity of a 200-4R. Both converters drive excellent and you wouldn't know the difference till cruise speed
When discussing higher end converters, they are non lockup for strength. There is not enough room to have the lockup clutch with a performance stator. I have been working on a new converter and stator design for six+ months now that will be lock-up, 3 bearing design and will perform like many of the higher end converters. The market has been asking for this option.
To run a NLU, a NLU valve needs to be installed in the transmission as well as removing the checkball in the input shaft. What this kit does is direct the fluid correctly thru the pump to the converter and then out to the cooler. A lock-up converter has the fluid enter in reverse of apply to lift off the lock-up clutch and then charge the converter. When lock-up is engaged, the fluid direction is reversed and fluid is pushed against the lock-up to force the clutch on with no fluid exit. The extra oil is diverted in the pump to the cooling system. Returning oil from the cooler is the oil that lubes the transmission.
Using either is a preference to a point. Many customers prefer the NLU when in the mid 10's and faster. When using an aftermarket computer, many like to use the NLU. This information reflects my converter designs, 3021, 3521 3017, 3018 and pro billet 9" diode converters, ect. Again, any questions feel free to contact me.