Lady Fitzgerald said:
I personally feel no one should use MSE. I used it for several months and was very disappointed with it. It simply doesn't do an adequate job of protecting from viruses. Except for when it first came out, it consistently ranks amongst lowest in professional antivirus program tests. Many geeks like it because it has a small footprint and a low profile but that is of little value if it will let something through. Most also use a good antimalware program, such as Malwarebytes Antimalware to compensate for MSE's weaknesses but one should never depend on a secondary program to be a first line of defense (although MBAM is an excellent second line of defense). That's like justifying driving with bald tires because you have a good spare.

For a business with 800 users, you need to bite the bullet and shell out the shekels for a good enterprise antivirus program or suite. Most, if not all, free AVs are for personal use anyways. Keep in mind that the cost of a good AV program or suite will be tax deductible. I'm not very familiar with enterprise AVs other than Symantec Endpoint and McAfee and do not recommend either one of them.
Well since they are enterprise, it may be slightly better. But if their home AVs are not good, there is only a slight chance that the enterprise version is any better. (My opinion, no offense to those that use it)