Robin Wong compared the two lenses.

How good is this lens for Astrophotography? Check out the video!

Amateur Photographer reviewed the Olympus 25mm f/1.2 PRO lens and concluded:

While Micro Four Thirds isn’t the most logical choice for shooting with shallow depth of field, for users interested in this kind of work there’s little doubt that the Olympus 25mm F1.2 is the best option available at this focal length. Indeed it’s a prime example of how comparing lenses on core specifications alone doesn’t tell the whole story. It may not deliver the same degree of background blur as you can get with larger formats, but it goes some way to making up for this by rendering that blur in an especially attractive fashion.
Given its price, this clearly isn’t a lens for everyone. For the majority of potential buyers, it’s impossible not to conclude that the Panasonic Leica 25mm F1.4 represents better value for money. It’s smaller, half the weight and half the price, while the latest version is weather-sealed. But then again, this has always been the way with ultra-fast primes. For those who can afford it and take advantage of its particular qualities and strengths, the Olympus 25mm F1.2 is a pretty special lens.

The 25mm PRO lens has $150 off till October 3th at BHphoto, Adorama and Amazon.