There's the old saying that goes, "If it seems too good to be true, it probably is."
But in the case of MSE, I think it is, in fact, all that it's cracked up to be.
I have run the gamut over the years (paid lots of money), and I'm gonna stick with it.
It's unreasonable not to trust it because it's free; other free ones are very popular and highly regarded.
Maybe there's suspicion because it's Microsoft? Look. Do you really think MS would unleash a product on the world that is going to allow all those nice new computers with Windows 7 to get infected? C'mon.
I think the main concern, if that's the right word, is that it's so simple. This is by design, of course. No endless popup windows, no deep tweaks, no nagging, no nothing. Just that little green castle with the check mark.
I have run every online test I could locate, and MSE found each and every threat and nuked it. It even found trojans in downloaded music I have had stored for years.
I like it.