Performance Improvements
In version 1.5.0, we did a lot of adjustments, mainly regarding memory allocations.
The details can be found in the Release Notes.
Some of them might affect users' customized code, especially if you have a custom command that overrides its GetOutput method, as now we use strongly typed outputs, where we should no longer cast our output into the object (System.Object) type.
This is not only less boilerplate-heavy, but also faster since we no longer cast into object which causes allocation due to boxing.

Check out the full description in Creating Custom Command Type.
Bug Fixes
The previous update (1.4.0) has a major bug which causes a project not to be buildable, which now has been fixed. This also includes other bug fixes which can be found in Release Notes.
New Features
In previous versions, running a sub-flow was quite confusing since the sub-flow exits once the flow from the default outputs is exited, even if there are still other parallel flows from non-default outputs running. So now, Sequine Flow provides an Exit command as an alternative to explicitly specify when to exit a sub-flow and return to the parent flow.
Check out the full description in Sub Flow.
