The circle currently spells its name "Twin Box" on both its website, blog, link banner, and formal credit images. The "TwinBox" spelling is stylistic and is not the formal circle name. Consequently, I am adding "Twin Box" as a tag and downvoting the stylistic spelling of "TwinBox".
The use of spaces in english names as opposed to the way spaces aren't used in japanese often leads to these stylistic differences in spelling of names. It doesn't help that some online sellers such as Toronoana may or may not remove the spacing out of the romaji version spelling. Even the mugimugi doujin database has both spellings for the same circle and thus duplicate circle entries which will be merged once I submit the errata so the database will eventually only have one circle entry "Twin Box". If you've ever looked at the errata section in the mugimugi forums, there are thousands of database entries that needed corrections typically because the automation bots accepts input from established online sellers as "truth". Thus, whenever staff at the major online sellers make a typo, don't use a space, or use engrish, that results in additional fun entries at the database.