Good info to add. Thanks.
We have used similar ones with generators, and they work, but you are correct they are a solar product first.
ETA:
As you're taking about manual, why not just have an additional service breaker put in, upstream of your panel, and add a 240v plug in between the additional breaker and original, and then just plug your generator in after isolating the house? A generator of that size will have a 240 source (at least ours do). Then use your normal breakers to serve what you need.