I used this Beta version for a few days but it was giving me a lot of splash screens on startups. Had to roll back. Anyway, MSE is a competent AV and I use it alongwith Malware. That is it. MSE also has definition updates which can be downloaded offline and just installed. So one can start off with the latest definitions. A lot of AVs do not have this feature. What about Forefront. Is it client (win 7) or server based.
Strange that you gets splash screen on startup. I use MSE one several computers now, and do not get any splash screen, and I do not see that MSE starts. The only time I see MSE is when it's find a virus/spyware/adware... I think Forefront is a centralized AV, you need it to run on a server on your network, but I'm not 100% sure, have not tried it yet.
This beta breaks iTunes syncing with any iDevice... you need to turn off "network protection" to make it work again... had this issue for months (since start of beta), figured what caused it just recently.