These are the in-progress versions of Sublime Merge, and are updated more frequently. Feel free to use them, but keep in mind you will be running less tested code, and you'll be seeing many more update notification prompts. Each release will normally have a topic in the forum.
Sublime Merge dev builds are currently available to everyone, but in the future will be available to licensed users only.
Sublime Merge may be downloaded and evaluated for free, however a license must be purchased for continued use. There is currently no enforced time limit for the evaluation.