We have previously been using a custom similarity plugin to meet the scoring needs of our application. It was pretty simple as all I wanted out of it was to ignore TF/IDF so I could compare scores across indices.
In the version 6 release, I have noticed there is a new option for Scripted Similarities. I believe this was added to meet the needs of people wanting to continue using the soon to be deprecated default TF/IDF similarity. However, I can see it perfectly suites my needs also.
I would very much like to get rid of custom similarity plugin, as it is a bit painful having to constantly maintain it with each new release. Before I switch from that to the new scripted similarity, I just wanted to know whether there would be any performance difference between them? As annoying as the plugin is to deal with, I wouldn't like to get rid of it if it is slower to process the scoring using a script.
Also, are there plans to add better API support for ScriptedSImilarities in Nest?