So, if I understand this correctly: The RB-1 has a ratchet for stitch length adjustment, the RB-3,4,5 have stitch length dial ?? That's really the only main difference ??
Reason I ask: I found an RB-1 on craigslist for $800.00. Not a horrible price, given how expensive these are, and only one owner (hopefully a light handed careful one). I really have no frame of reference for whether or not that's a "great" price, but supposedly it's to fuel the costs of a wedding. So, I might not negotiate down much from that if that's the truth.