Nice! Always love to see some personally engineered redstone contraptions!

If I may offer suggestions:

• You can increase the depth of the pit and line it with trapdoors so they’ll still pathfind in.
• You can use pressure plates for autonomous activation as suggested by other commenters
• If you have or can find some slime making the pistons sticky-pistons and having them move solid blocks should make the mechanism more dangerous to the mobs.