They were not going to ALLOW any blade that locks. Note box cutters lock. If you have ever used a knife, a locking mechanism is what makes a knife safe to use. A knife without a locking blade is almost always more dangerous to the wielder than the foe. Only thing a non-locking knife is good for is cutting apples.
They are not engineered to handle that kind of constant abuse. Downshifting without rev matching can be extremely taxing on the drivetrain, particularly if you are moving from an engine speed of 2000 RPM up to 6000RPM.
Synchromesh gearboxes removed the requirement to double clutch, they also made it possible to downshift without rev matching, however it is still rough on the drivetrain to send such a large impulse through the system.
Wouldn't such a system make toe-n-heel impossible? While most drivers of a manual do not know how or even why to do such a maneuver, it is required in order to properly downshift a manual transmission. If you do not rev match when downshifting it not only makes for a rough ride but is also very rough on the drivetrain.
If you sell diamonds, you cannot expect to have many customers. But a diamond is a diamond even if there are no customers. -- Swami Prabhupada
