Jeff, what is your expected daily mileage/commute with the car? If it's a short haul runner you may not even need 240V. I charge our EV 16A@120V (and we do have 240V in the shop as well) and it's fine for 99.9 % of our needs. I only charge in off peak ours, so 7pm to 7am. In the summer we only charge it a few times a week, more in winter as you'll use a lot of watts for heat in cold climates.
Since adding the 240V outlet, I've used it once for testing..that's it.
That unit you linked to just plugs into two outlets on separate sides of your panel (it won't provide 240V otherwise). However, at the 80% rule, it won't be worth it as you'll only get about 12A@ 240V usable. Using more for extended periods will exceed the design limits of a typical 15 amp circuit. Like everyone has already suggested you're better off just doing another run, or having a sub panel put in your garage with one feed.
Use this to figure out what you actually need for current/voltage :
https://evcompare.io/charging-calculator/
For example, 16A@240 V will add about 25km/h of range, or about 15 miles each hour of charging to a Model 3 AWD. Most EVs are very close in efficiency in similar size classes. It is a bit more efficient to charge for less time (less time running overhead), however I prefer to go super easy on the EV pack and charge it slowly...particulary when it's in the - 10C or lower range in the garage. It's also pretty clear in the research to try and keep the lithium pack close to 50% charge for longevity. I normally stop a charge at 80% unless I'm doing a long trip. Hence the need for a ton of current may not make sense unless you actually need to add range quickly.
