Frankly, I'd say it's probably not worth it for most users. I bought it to see how well it sped up the heavy-duty tasks I do on my OS 9 MDD, and you saw the results: overall better, but not as much as I hoped. Mine was bought new from Sonnet for around $600, which is now more than what the MDD is worth, and now that they are out of production you can expect to pay more if you can find one at all. Unless you have a lot of cash burning holes in your pockets, for most tasks, the improvements will be noticeable but only minor to moderate.

The last bootable OS 9 G4 was the single processor G4/1.25 released in 2003 with FW400 (a quiet closeout by Apple to capitalize on remaining pent-up OS 9-compatible hardware demand). Note that this model succeeds the 2002 dual 1.25GHz FW400 (which is what I have), which is the most powerful, but was not the last.