The problem with simultaneous submissions is that you're firing all your bullets at once. If the story has a problem, you won't have a chance to work on the problems, or problems, between submissions.
My experience is that good stories don't need to be submitted to several mags at once, and poor stories are just harmed by it.
Writers tend to want to use simultaneous submissions because they think it takes too long to submit to one magazine at a time. They need to stop worrying about time, and worry about selling. Selling is easier when you get editorial feedback while still having good magazines remaining that you can submit the story to. Such feedback is useless, if you've already blown through all the good markets.
Submit to one magazine, sit down and write another story, submit it to one magazine, and so on. It won't be long before you have enough stories circulating that you hear back from one market or another every week.