I always assumed that straight-ankle locks were relatively safe compared to, say, heel hooks. In all the tourneys I've been to, they're the only leg-locks allowed in beginner divisions, probably because there's less risk of serious injury from a white belt exploding on the submission.
This isn't the most educated opinion, but I think you can adopt a wait-and-see-if-it-actually-hurts approach to straight-ankle locks without putting yourself in unnecessary danger.
This isn't the most educated opinion, but I think you can adopt a wait-and-see-if-it-actually-hurts approach to straight-ankle locks without putting yourself in unnecessary danger.