One can be safe w/out AV as long as they made decent setup with other ways and follow best practices. My view for AV is basically fail-safe when I did sth stupid. So I used WD when I was testing Win8 with all security measure available in Windows including many registry tweaks, SRP with custom ACLs, fully restricted Chrome, EMET with custom rules for ASR/EAF+, etc. I don't recommend common ppl to use MSE as exclusive defense line, but it can be good supplement when you're already safe by other means. As to update cycle, actually it's not much matter as long as internet connection is available since they use cloud.