I would take a y/g thuri over a naniwa stone at the same price. What thuris bring these days, though, I wouldn't pay.
I'd buy four small japanese stones described as finishers from a stone dealer, and sell the three I didn't like that much. One of the four would probably be finer than a thuri.
(or I'd buy a translucent arkansas).
If you're used to working with synthetics, you might find that you don't like a thuri and don't get much out of it. Or you could go the other way, natural stones just work differently than synthetics in terms of how they cut and it makes you feel more involved.