A lot of BJD-fans buy them as a substitute of those beautiful resin dolls when they don't have the will to work to afford one; and Obitsu-dolls are often frowned upon in the BJD-community.
"Ohh, cool, he's pretty. I got an Obitsu, we should totally do a photoshoot together!"
"... Obitsu '>_>"
In a more slang sense, the word is often used as a verb. To "obitsu" a doll is to replace one or more of the body parts of an existing company-made doll with Obitsu items.