The Arro and Rainmaker aren't that similar. The Rainmaker has been criticized for sounding a bit sharp and edgy. I haven't heard the Rainmaker in a while, but I did hear both side by side a while back. I liked the Arro quite a bit more.
Totem designs each speaker individually. There's no line, so to speak, of small, medium and large of the same speaker. I think Totem suggests the Dreamcatcher as a surround for the Arro, not the Rainmaker. Possibly the Mite, but most likely the Dreamcatcher.
Did I mention I'm a huge fan of the Arro?