I've used both and they are about on par with IQ, a slight edge to the Panny. The Panasonic is nicer/more convenient if you plan on doing video but no, I don't think it's worth 2x the price. I found a new one for just slightly more than the Oly and am happy with its performance up to about 160mm (I admit to being a pixel peeper).
We have both in the family and as someone has already suggested they are very close in IQ up to 120mm but after this the Pana is definitely better than the Oly.
Is it worth the extra? On Oly bodies no. On Pana bodies - depends.
Yes it handles better than the Oly at the long end because of the fixed length (also may mean less dust gets sucked in with use) and takes the same 46mm filters as the 25mm, 14mm etc so could save on filter purchases.
I don't think the P40-150 is quite as good as the Oly or P45-175 so if you are a GF/G/GH body user it's not quite so clear and would depend on how many filters you use or how often you use 120+.
For us (EPL-3, EM-5 and G3) we might have been better with Oly40-150 and Pana 100-300.
I have the EP5 and the 45-175 focuses very quickly. I like that it's internal zoom and find that i use the zoom switch often when photographing wildlife. It's very convenient and quick. There are some decent prices on ebay for used. What are you planning to photograph?