One should not use "drop-in" when they have their own query language and seemingly input shape for the /search endpoint (which is also different from Elastic, of course) https://manual.manticoresearch.com/Searching/Full_text_match...
It sounds like they're really targeting the logging search store part of ELK, which can be a perfectly fine objective, but no need to mislead audiences since they will find out and then you've made an enemy