Nobody's building Uranium bombs nowadays, not even North Korea. And the laws of physics work the same way in Persia as anywhere else.
The disadvantages are obvious, natural Uranium contains about 0.7 percent of 235-U. With great effort, you'll get around half a percent out of it. The remainder can be converted to Plutonium in a nuclear reactor, which is much easier to separate. A reactor could be something as simple as the Chicago pile, natural or low-enriched Uranium, and graphite as moderator. The pioneer work was groundbreaking in the 1940s, now it's downright primitive technology.

If Iran were pursuing nuclear weapons in earnest, they would've done it long ago.