No, there's no saftey risk to not venting to the outside but if you have the option to vent out then that's what you should do. Recirculating hoods are better than nothing but you really want to vent the smoke, grease, heat, steam and odors to the outside and not recirculate them in your kitchen. There are dampers you can put on the vent pipe to prevent cold air from entering your kitchen.

I only saw one Ventahood where I could try to figure out if the cleaning or the more raw underside would bother me, and it was not connected to power so I don't know about their sound level. I've heard they are quieter and I've heard they are louder. I think the looks of the cages vs baffles would be more of an issue for me. While I was trying to decide whether that was a bit "raw" looking, I was led to a guy at the place where I bought my appliances who said he'd seen and heard both side by side. He said the Best by Broan was better for sound and operation, so I went with it. Very scientific, huh? Unfortunately, buying a vent is like that. I have a 1200 cfm model with an external blower and got the baffles. The blower sits just above my sink on the opposite side of my kitchen (better than the toilet or shower straight above --LOL) and it is quiet when you are outside. I'm not sure that in my set up the remote blower made that much difference. If I'd have another inch or two, I'd have been able to put in a silencer. Most of the time, I run the vent on the lowest setting or up to about 1/3 power -- rarely over 1/2. At that level, the fan on my ovens is as loud. You barely hear it away from the vent, but you will standing right under it. At full power, you will hear it, but even then it is not as loud as the ineffective downdraft my last cooktop had -- with only one speed. If you turn it on when you first start cooking and run it higher for things like fish, popcorn, bacon, you will not smell them all over the house. I made 120 bags of popcorn, both on the stovetop and in the microwave (bags opened under the vent)one afternoon. I delivered them to the school, came home and could not smell any popcorn. Maybe it could be more perfect, but I'm happy with my choice.

There is a thread on here about the VaH ARS system. I think it is here (from notes -- not checked):: https://www.houzz.com/discussions/2347276/vent-a-hood-ductless-ars-range-hood-update#n=65 Opening a single window will spread the grease around just as well or better than a recirculating hood that is crippled with no or slight filtering. Opening one window and using a large window fan in a transverse window (with the cooktop in between) might be better than a non-performing recirculating hood. Please reread my comment. Any hood used has to have adequate performance or it is a waste of money. " Shelly Miller, PhD, a mechanical engineering professor at University of Colorado Boulder, told us that if you don’t have an exhaust hood over the stove that vents directly outside, you’re better off opening a window or running an air purifier." I don't know the date of this telling, but it should be obvious that a grease filter will reduce the amount of grease recirculated, and a charcoal filter (also part of the ARS) will reduce odor. An air purifier that could filter at a 300 CFM rate would be quite the beast; at least the same scale as the ARS. If the filter takes seemingly forever due to its low flow rate, then filtering works mainly by letting the grease aerosol particles settle out on the surfaces and fabrics. Absolutely the recirculating design needs mesh or baffle filters (mesh may be better at low air speeds) or the VaH approach of centrifugal impingement using the blower -- and -- charcoal filters for odor removal. Serious grease particle removal might require stacks of different filter devices. These are available for commercial purposes. [all I have time for this morning]

Wolf hoods and inserts have controls for Wolf blowers, which I believe are still made by Broan/NuTone (although there may be additional imposed manufacturing requirements). In my experience (now somewhat dated) these blowers are induction type and use simple continuously variable controls. That is what my configuration is. In general, all two-wire w/ground directly-powered ac induction motors can be controlled by such devices. Suppose, for example, you alternatively wanted to use a ModernAire hood using an in-line Fantech advanced motor that uses a 10-volt control signal. Then either ModernAire would have to provide a suitable control built in to their hood, or obtain one from Fantech and integrate it into their hood. When using a vent system made of parts from disparate companies, you or some experienced HVAC sub will have to deal with achieving compatibility. In my view, it is non-optimal to address MUA after addressing the hood system. The two have to work in concert. Yes, hood requirements have to be calculated first to filter the hood components into an acceptable group, but then other considerations in concert with the hood system requirements drive the MUA requirements. These other considerations include architecture for integrating and ducting the MUA, presence of potentially back-draft susceptible combustion appliances, and MUA complexity. In some cases the MUA will need a control system that takes information via electrical interface with the hood system, or via sensor measurement of the hood system state.