I looked at the photozone review of this lens. A direct quote from their review:
That said it is still interesting to look a bit behind the scenes by using an "unsupported" RAW converter like e.g. RAW Therapee. This converter reveals the native barrel distortion level of about 5.8% at 12mm. This is excessive ...
Which suggests that the lens should be used according to the manufacturer's instructions. mFT lens compactness is achieved in part by handling distortion with software correction in addition to "hardware" correction, with the manufacturers' stated intention being to the apply software distortion correction: either in-camera, or with the provided RAW conversion software, or in software like Lightroom or ACR, which can do it using the lens profile information that Olympus and Panasonic include in their raw files. Photozone seems aware of the latter, by its use of a non-mainstream converter specifically to avoid those corrections.
As to this:
... in-camera correction comes with its own problems when the image is stretched and/or compressed to remove barrel and pincushion distortion.
to the extent that this is a problem, one should measure and assess the degree of _that_ problem, by looking at files that have been converted in the intended way, with correction. Otherwise, what photozone says is a bit like complaining about food poisoning after ignoring the label warning people not to eat something raw.