We Never Know
No Slack
How would you know? Do you have accurate carbon monoxide meters that display how much CO is in the air? If you do not then you have no way of telling how much gets vented out.
And as to those gas heaters, they do tend to be needed to be used in well ventilated rooms. The heaters themselves have to be well maintained:
Are Vent Free Natural Gas Heaters Safe?
There are a lot of potential problems with those and I do agree that if one bans new gas stoves, those would need to be banned as well.
If it takes away the smell of onions and vinager, I think that shows it work quite well