The non locks are a custom, purpose built converter. You can start with a clean sheet of paper and do about whatever you want with the design. The lock-ups require the design to be around the lock-up assembly which limits core choices and stator design. This can limit the spool and efficiency of the converter. Some combinations work well with the lock-ups because they fit the rpm range and spool requirements of the combo. The non lock can be used on a much more wide range of combo's since it's so adjustable.