The window unit linked at the top doesn't appear to do heat recovery. Most of the decentralized single-room mechanical ventilation heat-recovery (MVHR) units reverse their fans every 60-70 seconds in order to operate their heat exchangers, such as this example.[0] That period should be long enough for the exhausted air to disperse far enough away outside that it won't just be sucked back into the house, unless the exterior exhaust is positioned in a really weird spot outside where wind is minimal and the air can't effectively disperse. Alternatively, they can also be paired with another unit so that one exhausts air at the same time the other brings in fresh air, allowing better airflow across/within the room.

The problem with this approach is that once you start ventilating multiple rooms with these small units (figure $500 per room with a single unit, twice that if two), the cost rapidly approaches that of a centralized unit with ducting. But if you're just looking to ventilate a room or two, they're likely a very cost-effective solution. I could also see them being used on a first floor living room/kitchen in conjunction with a centralized unit ventilating upstairs bedrooms with the ducting run through an attic. That'd probably be cheaper overall than trying to run an intake/exhaust duct downstairs or installing units in each room. Plus, each exterior penetration increases the opportunity for uncontrolled air leakage and, most importantly, water.

0. https://www.bpcventilation.com/bsk-zephyr-single-room-heat-r...