A little suggestion to add the ability to define a custom effect for simplistic mod compatibility. The idea would be to add a button or icon (probably in the bottom right to balance out the UI) that would open an empty text box so you could manually type in an effect. e.g. sizeshiftingpotionst:shrinking compared to the default Minecraft effects like minecraft:speed. This would allow for a lot of other interesting parkour uses for those interested in doing so within modpacks or with specific mods.

Also, it might be interesting to add a button between the Duration and Level input to toggle true and false for the [<hideParticles>] parameter.