Real ERV/HRVs have ducting ports in both sides, and installing all the ducting and electrical is far more expensive than the $500~1000 the unit itself costs. That's why they're uncommon: Install is expensive and painful.
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...
Are you referring to the ports on the interior or exterior?
Amazon reviews for the Bionaire reported both energy savings and air quality improvement, so it worked for some people.
For homes, there are DIY full-sized HRVs, with custom ducting, https://ecorenovator.org/forum/showpost.php?p=26861&postcoun...