The biggest issues is most people are ignorant to the subtle nuances of leg locks. Its not the submissions themselves, but rather the positions of control that are important to develop at lower ranks. Learning and developing the skills necessary to transition to the positions of control and escaping them are the real foundation of leg lock development. Its funny how one of major guidelines of Jiu Jitsu is position first then submission however its overlooked when it comes to leg locks. Once you develop your positions of control and your transitions to them you have a number of submissions to choose from:
Straight Leg: Calf Crush, Achilles Lock, Foot Flex, Hand Pressing Foot Flex, etc.
Rotational: Heel hook, Hand Pressing Foot Flex/Heel Hook Combo, Toe Hold, Hip Lock, etc.
and thats just form your standard leg control positions: 50/50, Inside Controls (Clamps, Wedges, Knots, Splits,etc.)
Theres no reason why white belts can't be using straight leg submissions, as long as there is an emphasis on positions and transition.
Respect your training partners and the potential dangers of ALL submissions and you can train with leg locks as you would any other submission.