I agree with what's been written so far. The BuzzPro and InfinityPro both use the same electronics and user-interface implementation (thumb-wheel voltage adjustment), so the actual vaping experience should be identical.
Some other differences:
The BuzzPro is heavier, shorter, and more beefy in size. The InfinityPro is lighter, longer, and sleeker.
Being larger in diameter and a bit stubbier, the BuzzPro has a steadier footprint. It won't fall over just because you look at it funny. The taller, slimmer IPro is less stable when standing upright and will fall over if the table is bumped. This is more pronounced when using tanks, which make the IPro seem a bit top-heavy.
The extended 510 connectors on both units make for a less seamless aesthetic appearance with tanks, because of the 1/4" gap between the tank and the body. Tube mods with a flat top (such as a LavaTube or Bolt) look very good when paired with tanks of the same diameter. 5-6ml tanks are visually better-suited to the BuzzPro, while 3.5ml tanks complement the IPro nicely.
The various kinds of protection built into the circuitry and tube bodies of both units is impressive, and---given ECF's recently renewed concerns about battery safety or lack thereof---very meaningful. Peace of mind is a good thing.