4000 really isn't much heat, it would warm hands held over the flames, but not really contribute to the heating of the room.

I would go for a proper heater, then have one of the little, for effect only, fake fireplace ones for the visuals if wanted.

Not sure what your budget is, but the ultimate combination of these would be a Dickinson propane model. They are pricy, but built to last forever, are quite efficient, very esthetically pleasing, and direct vented (so none of that pesky dying in your sleep due to low O2 or CO poisoning!).

A strong thing to think about when choosing a heat source is fire danger. In a tiny home, a small fire can quickly become lethal, so ones like an infrared heater have very directed heat which require a lot of safe space in front. Also, even with the small ethanol fireplaces like you've linked, make sure you crack a window or something, especially if burning for a longer period, as they really do eat up a lot of your O2 and replace it with CO.

Lastly, regardless of what you go with, make sure you get a GOOD CO detector, just a smoke alarm is not enough! As an EMT I have seen way too many dead pets, kids, adults due to poor ventilation of a combustible heat source in a small space.