How safe are ventless gas heaters indoors?

there’s one in the home we’re renting, and there’s a CO detector plugged into the same outlet, (so about 6 inches away from the unit). The furnace may or may not work, it hasn’t been used in two years, we haven’t tried it yet. Is it safe to use the ventless gas heater as the main source of heat? It’s a small house, not very well insulated, and we’re poor, so cost is a big issue.

I read that in some states that it is illegal to use a ventless gas heater indoors? Or was that just back in the 80’s when they weren’t as well researched yet?

Also trying to decide on getting some kind of heater for the bedroom, (it’s the farthest away from the scary ventless gas heater) and we currently have a little space heater that just plugs into the wall, but I’m being told that oil water heaters are better?

Basically we are poor and live in Michigan and we dont want to freeze to death.

Any ideas?