Since ESSL is more or less a subset of GLSL x, using Shader Builder in OSX is a pretty good way to develop shaders. The only difference would be in the accuracy settings, but you will not get the proper result for this until you try it in the system.
There are solutions - malideveloper.com has an Eclipse plugin for shader development, but this is for Linux / Windows.
So my answer is:
Use #ifdef SHADER_API_OGLES20 for accuracy. Try not to use too strange built-in functions. Dump the compiler log when developing.
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