“Since image quality of each focal length is [as] strictly controlled as prime lenses, this lens can be seen as equivalent to five prime lenses: 20mm, 24mm, 28mm, 35mm, and 50mm,”
a “Holy Grail” lens for Panasonic videographers although it is expensive and somewhat heavy
covers 20-50mm in FF terms - this is a unique and very useful range which is not covered by any full frame lens as most systems have 16-35mm or 24-70mm lenses
significant field curvature can make corners out of focus at 10mm and 25mm - the Panasonic Leica DG 8-18mm f/2.8-4.0 ASPH lens is much better in the corners at 10mm but not as good at 18mm, while the Panasonic Leica DG Summilux 25mm f/1.4 ASPH lenses has similar field curvature and once corrected, the corners are not quite as sharp wide open and has more CA than the 10-25mm at 25mm.