I signed with Musa very early on. My novel was published November 2011, and it’s sold 32 copies. I’d be surprised to learn more than a handful of those sales were due to efforts outside my social media announcements, website, BLOG, newsletter, interviews....
I’ve tried to monitor this thread when it’s actually on the topic of Musa, and my views and experience probably reinforce what most have already surmised. Musa will edit your work with low paid editors who feel they’re building their credentials by working at Musa. You might luck out, you might not. Musa does a good job with cover art and text layout. They put the novel up for sale and make it available for purchase at the major sites.
My primary complaint, like most of the authors I've read here, is the lack of promotion/marketing. Musa maintains a current website and BLOG, posts on social media, and claims to send new releases to an extensive list of reviewers. I suspect they do indeed send releases to reviewers, but it seems resulting reviews are very limited. I had one review from Musa’s efforts. Beyond that, they regularly offer advice and pointers about how to market your own book. Grumblings about lack of sales or marketing are immediately turned around to point responsibility at the author for not marketing it better himself.
Authors' expectations are as widely varied as their reasons for publishing in the first place, so I'll not chime in on how many sold copies qualifies as successful. Based on my experience, Musa is a poor choice if an author expects a publisher to not only put out a good product but also to stand behind it and promote it and depend on it to make sales. On the other hand, if an author wants a story or novel e-published and put up for sale with a nice cover and no costs to the author -- and that’s all the author wants -- Musa could be a good fit. I don’t know enough to speculate on their longevity, but, like others, I wonder if they have enough sales to survive very long, and I recommend prospective authors make sure the reversion clause in the contract suits you.
kap