Since getting unhappy girl early is very important in farm decks, using Rai-Mei will essentially make it feel like you have 6 unhappy girls in your deck. It's also useful for deck thinning by attacking into your opponent's monster if they have higher attack.
No. Actually, there's a similar cards, but a searcher for level 1 or 2 machine, warrior, dragon, aqua, spellcaster, or normal monster. you can see the details here: http://yugioh.wikia.com/wiki/Searcher