I like that it blocks messages from certain websites, which saves me time in having to delete them later or move my email account away from those domains.
It also gives you an option of blocking keywords and links as well so if someone tries something suspicious with your inbox (like say they send out thousands upon thousands of emails) this can help block some of their efforts before any damage occurs. The only thing about spameo i dislike is how slow at times when loading up pages within gmail while using other tabs / windows etc. So far there are no complaints! There may be better options but we use Spam EO Pro by OJ Technologies because our clients require us to have anti-spambot software integrated into all client platforms - desktop/mobile device OSs.