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My previous company was a digital consultancy that used macs exclusively, which was a joy for me although running excel in parallels was tedious. Powerpoint was allowed only if seconded into a client who used it, core work was done in Pages as stipulated by the style guide. For quite a lot of hires a quick half day or 2 hours to get used to it would have been really helpful, especially if it could be referred to later.
I think the issue is more that those who are willing to pay to go on a course are probably those who already know how to use them. If you're interested enough to pay to learn you probably already have the basics.
If you're planning to market it to businesses who have employees using Macs then that would be a different matter. I imagine (well I know there are, I've been to some) there are a reasonable number of people who've ended up at some "creative" firm who are forced to use Macs as the company doesn't want a mixed network of Mac and PC.