To add - yeah, I guess this isn't directly connected to the coax (hard to tell) and they claim capacitive (lossy?) coupling as opposed to the direct connection.
The 6 meter dipole is not directly connected to the coax, hence the "parasitic" coupling. Just wondering how well that works.
I was wondering the same thing so I modeled this antenna from both the 6m and 10m perspectives.
In these models, the 10 meter antenna is mounted 18 feet above moderate ground, and the 6 meter antenna is a few inches above that. Also, these antennas are made out of T6 aluminum and tuned for low SWR, not resonance.
For these models I will show the 6 meter antenna info first, and the 10 meter second.
To start, lets look at the general data.
Here we see that the 6 meter parasitically fed antenna does have more losses due to the aluminum material I used in the model. Of 100% of the power being fed to the antenna, at 6 meters 0.36% of that is being lost compared to 0.1% on the 10 meter antenna from the aluminum being used in the antenna itself.
However, after things like ground losses are factored in, the 6 meter antenna more than makes up for this difference, with 71.28% of its signal making it to the antenna's far field, while the 10 meter antenna has 63.8% of its signal making it to the far field.
So, according to modeling, the answer to the questions on efficiency of having a parasitic elements of a different band, their doesn't seem to be a problem with efficiency.
Next, I'll show the current distribution.
One thing to notice here is on the 6 meter model most of the current is flowing on the parasitic element. The parasitic feeding of the 6m antenna is working very well.
Next the SWR curves for this antenna.
Here we see the parasitic element can be tuned to present a low SWR, however, the 2:1 SWR bandwidth on the 6 meter band is not very wide, in this case covering about half of the 6 meters band. This low SWR point can be adjusted to other parts of the band by adjusting the parasitic antenna length.
I also want to point out that once you get the parasitic element length for the antenna to show resonance where you want it, you can actually fine tune the R variable at resonance (and by extension SWR) by moving the parasitic element closer or further away from the driven element. Because of this I was able to get the low SWR point of the 6 meters band below that of the 10 meters band.
Now for the gain.
You have all seen enough of this type of plot, so I will let you draw your own conclusions...
The DB
