For a similar, official weapon, see the spinning sword from Secrets of Sarlona, which is similar to a one-handed spiked chain, minus the actual spikes and plus a sword hilt. It has 10’ continuous reach, and a 19-20/×2 critical threat rating.
Note that no official weapon in the game has a base threat range of 17-20. Wizards of the Coast would have considered that overpowered and problematic. I find crit-fishing to be a wasteful strategy most of the time, which may work somewhat better with a 17-20 base, so I wouldn’t say overpowered, but I have to agree that it’s problematic: every crit-fisher ever should always use this weapon. The 17-20 threat range trivially blows any other possible weapon property out of the water for such a character. Attaching it to 10’ reach, presumably continuous, makes for what is quickly becoming the be-all, end-all weapon that basically every character should use—rather problematic for a game that wants to support all sorts of different characters.