In case you haven’t figured it out yet, part of the purpose of this blog is to offer less expensive options in the m43 world. OM System’s newest lens is a worthy addition but still costs at least $800 USD new. I suggest you try the Leica D Summilux 25 mm f/1.4 made by Panasonic for the 43rds world, introduced in 2009. There are now many used copies available for less than half the price of the OM System Zuiko Digital 20mm f/1.4 PRO.
The Leica was right/left/left. By my tastes it seems to have the edge of performance over the Zuiko.
The Zuiko does focus faster and quieter. From the closest focusing position it focused on the ISO 11223 chart instanteously (recorded as 0.3 s) whereas the Leica took 0.9 s. But realistically both lenses focus fast and accurately.
In summary, the Leica is less expensive, allows you to proudly display the Leica name on the lens, and may produce the slightly more pleasing image (this being highly subjective). The Zuiko is lighter, smaller, quieter and weather sealed but more expensive.