Your two links are the same.

The glass shape of the Kobe has no capture area because the plume can leak out of the curved shape.

Having a sub hood area filter pack is a poor design when there is no capture volume, and its boundary protrusion downward further blocks the effluent from flowing into the filter

M Miller's comments are correct.

Much more can be learned from the many hood threads on this forum

Perspective on what is to be accomplished -- viz. capture and containment -- may be learned from the first dozen pages of the Greenheck Guide, available from:

https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf

Here is the correct link to the Futuro Futuro Moon Crystal hood https://futurofuturo.com/36-moon-crystal-wall-range-hood/. Between that one and the Kobe that the OP linked, the Kobe is the better choice. But you must get your hood in the 42" size, not the 36" size if your cooktop on an island is 36" wide. That was mentioned above, and that is correct.

Sorry, I would not choose a glass hood if possible, despite that they look cool. The glass looks greasy most of the time, it's like having to wash your windows. There is always a corner or a spot that you miss, and your fingerprints on there from trying to clean it. But I get that you want a light-looking hood over your island. Just be aware of that. It is STILL MUCH BETTER THAN A DOWNDRAFT.

If you go back in the the archives, you'll find basic rules how to compute the required CFM. And you'll probably find that 600CFM isn't going to cut it either. Let's say you followed the advice that was just given to you, and you sized the hood to be at least 42"×27" (even that is a little tight for an island hood, but I realize you want to keep things smaller). That gives you a capture area of 7.8sqft. You need a velocity of at least 90 CFM per sqft for a residential hood to work properly. That nominally gives you a need for 700 CFM.

But manufacturers cheat. They don't tell you the actual CFM that you'll get. Instead, they'll give you an unrealistically high number that is measured without any duct connected to the hood. In practice, you need to add at least 50% to compensate for inevitable performance losses (and that's assuming you have 10" ducts and a working make-up-air system). Now you're at over 1000 CFM.

This number would work, if you had a wall-mounted hood. With an island, everything gets more complicated. And you don't make things easier by having gas (needs more ventilation than induction due to hot combustion gases) or by cooking smelly foods in an open floor plan.

Also, your plan to use both downdraft and vent hood at the same time doesn't sound good. The two systems are going to fight each other and you'll end up having uncontrollable turbulences that make overall venting even less efficient. Don't do this. Get a properly sized hood and a properly size make-up-air-system, and enjoy that you won't have cooking smells in the rest of your house.

It is much more difficult to capture effluent on an island range than one against a wall. Neither of your posted options will work well.

More: https://www.gardenweb.com/discussions/5161173/hood-faq

Basically you want a very large hood, ideally at least 12" wider than your range in width and depth, a large containment area (a bunch of open space within the hood to contain effluent until it can be exhausted) and enough CFM's to function well.

Ruth wrote: "The Kobe is cheaper. We won't be using all 6 burners at the same time so figure 600cfm should be fine. Maybe we can use the downdraft along with hood when cooking on 4 burners...not sure"

I failed to address this sentence adequately. The primary two purposes of a hood are capture and containment. The capture part depends mainly on the hood overlapping the rising and expanding cooking plumes. Little capture results from the airflow of a hood that most could tolerate the noise from; there are some slight peripheral effects.. Capture depends on overlap.

Once captured (inside the boundary of the hood), then the problem is containment. This depends on the airflow (volumetric flow rate -- usually in the USA given in CFM). The required airflow is only indirectly dependent on burner BTUh or number of burners in operation. It depends on entraining the plume into the hood airflow and not allowing the plume to reflect off of the sheet metal and spill outside the hood. The plume velocity can be as high as 1.2 m/s and will retain significant momentum when it reflects off of the sheet metal, but it seems that around 90 ft/min of hood blower induced air velocity (roughly half the plume velocity) at the hood entry aperture is sufficient for baffle type hoods to successfully contain the captured effluent.

These facts imply that the full CFM performance of the hood should be 90 ft/min times the intake aperture of the hood (sq. ft.) to yield cubic ft/min.

The product value obtained from this multiplication has to be achieved in the presence of baffle pressure loss, hood pressure loss, duct pressure loss, and make-up air (MUA) pressure loss. These pressure losses are due to friction and turbulence. Blowers have a property of flowing less CFM when subjected to pressure loss, and blowers are also rated at zero static pressure (that is, hanging in the air). Hence, one has to take the value obtained to get 90 ft/min and increase it according the blower's pressure-flow performance, usually plotted on a graph and called a fan curve. See example.

If none of the pressure losses is known and no HVAC support is available, I recommend picking a blower that is rated at 1.5 times the CFM actually needed.

As for noise, there will always be baffle noise (typically a hiss) and other turbulence noise. The dominant noise is turbulence from the blower blade tips, and this can be attenuated by an in-line silencer (where room allows) operating with an external blower, or by running a higher performance blower than needed at a lower speed than its design point.

Thank you all for the detailed feedback and links. This has been very helpful.