|Olympus E-PM2 with Panasonic 20mm F1.7 lens|
Love the small size of this pen cake lens.
Make a camera like Olympus E-PM2 almost pocketable.
|10% crop showing purple fringing|
|Fringing removed in Lightroom|
My recommendation is to buy this lens if you want a small general purpose carry around lens. Do bear in mind the limitations listed above. If you want something smaller but wider, then the 14mm F2.5 is a better choice. For me, the size, low light performance and sharpness is more important. If distortion and CA is a worry, I will shoot RAW and correct in post.
At the moment, there is no other lens at this focal length, cost, size and speed. The closest lens in term of speed and focal length are:
Panasonic 25mm F1.4 - Sharp fast lens and better for bokeh, but significantly more expensive and larger.
Olympus 17mm F1.8 - Sharp fast lens, slightly larger, but again more expensive.
Sigma 19mm F2.8 - Very sharp, it is a slower lens and physically much larger, but at a bargain price.