The efficiency enchantment does not work on custom tools at all. If you add minecraft:digger to a item in a behavior pack, and have use_efficiency set to true, it won't work at all.
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Comments 2
I suggest you reopen this report as MCPE-100344 does not mention anything with the efficiency enchantment not working in the description.
Thank you for your report!
We're tracking this issue in MCPE-100344, so this ticket is being resolved and linked as a duplicate.
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