MSE seems like a good program but I haven't seen it put to the test yet, that is, finding or cleaning malware. A particular point in its favor is that its license allows corporate use. However, it's a management nightmare in an organization with many computers. Microsoft does state that it's not designed for business use.
I had one client with 6 computers running a custom application. The computers' system drives were small, and there wasn't enough space to accommodate their usual AV client. A staff technician had installed MSE on these computers as a temporary solution. I had to remote to each machine to exclude the custom application's paths and its many processes because the SpyNet feature that submits new processes to Microsoft would cause it to crash. It also happened that a crash would ruin an entire days' work, since the purpose of the software was result collection in a lab environment. So, it's convenient for home users, Might be OK for small businesses... not recommended in an enterprise environment. And I'm eager to see how effective it is against malware.