Any opinions on ventless fireplaces?

You are correct. It uses the same gas as your gas range.
It is a pretty way to add heat into a room.

I go for the functionality of a wood burning insert but that is not for everyone. Some people don’t want a pile of wood in their house.

I should add some “opinions” since you asked. If you are building a fireplace you should have a vent or damper you can close. Otherwise all you are doing is taking up a lot of floor and wall space for something as functional as a painting.
You should never run them for a long time due to condensation, and you should have a window or two open a bit to draw in fresh air.
The gas units are nice because you can simply click the remote or use your iPhone to turn it on and you have instant fire. That could be considered romantic for the first few times you do it
For the long term I like the idea of a real fireplace with a high efficiency woodburner If there was ever a disaster my unit can keep the house warm for a long time. And I can get rid of combustible trash.

I suppose that these are safe, but I worry anyway.

From my youth, I was taught that all fire needs a source of fuel (gas, wood, propane, etc.) and a place of exhaust. A gas stove uses so little gas, and is so pure, that the amount of waste product is minimal and dissipates in the air of the kitchen.

A gas fireplace has considerably more burners than a stove. My worry is that the combustion is not 100% (although close, like a stove), and there is enough residual unburnt gas that it could cause issues in the house.

But like I said, maybe I am worrying too much.

@elbanditoroso They have those burners adjusted on the lean side. They take in more air than needed and burn the gas making CO2 and H2O. Both are relatively inert. During the winter most homes up here can use the extra humidity. If there was any gas sneaking out unburned you’d smell the mercaptan, rotten eggs smell, that is added as a safety measure.
My biggest worry is that the combustion air intake gets restricted somehow, causing incomplete combustion and releasing CO in addition to the CO2 and water vapor. I have not taken one of those units apart so I do not know how they prevent it. But I’m guessing they figured it out.

WAY OUT THERE – - – >Here’s an option Wall mounted

How hard is it to add a regular vented gas fireplace to the main floor of a two story house? It has a basement. Do you just open up the roof no problem to put a vent?

Most new gas fireplaces use a through the wall short stack or chimney. Here is a EXAMPLE of what is used. You don’t need to add a brick chimney or an insulated stove pipe to go through the roof.

^^The link didn’t work, but I know what you mean I think. In my last house there was no chimney per se, but some sort of vent. Now that you make me think about I think it did just go through the exterior wall directly behind it. I wonder if you put a fireplace in an interior wall if then it has to go up to the roof?

Thanks!

My firenplace is on a centrally located interior wall. The chimney goes up through the attic and the roof. The flue for my stove in the basement goes up through a closet, attic and then the roof.

Sorry the link didn’t work.