OTOH, Bostonian's course sounds okay. I'm certainly in favor of anything that improves writing skills! Learning to avoid run-on sentences sounds great. I have not the slightest idea what this means, though:

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phrasal modifiers (including verbal constructions or finite verbs

That is complete meaningless blahspeak to me.

I wonder if this course has an actual teacher or is multiple-choice nonsense. Really--a good teacher who edits your work is what you need.