I’m really enjoying Gleam, there are some things where I would say my productivity is improved.
Particularly the annoying glue code and making sure errors are handled.

Obviously total productivity for a project is reduced as many libraries don’t exist. It’s always quicker if you don’t have to build things.
If your willing to write some erlang code to get erlang librarys into your project I would say you might be surprised at your productivity. I was.

In future it should be possible to provide better autocomplete with Gleam than with Elixir as it is capable of performing superior static analysis, but today there is no IDE like features in Gleam. It is on the backlog though

I would say that in languages like Elixir it is not that much of the problem as you quite rarely need to dynamically lookup the possible functions (as there is no “methods” in a way that it is in OOP languages).

About Gleam - for now I didn’t have need to test this out yet as I mostly focus on Elixir and Erlang right now and adding new language to the set do not seem to be feasible.