I did some testing in the house and even with the antenna in the middle of the room rather than next to a window I get 2 extra bars and can access the web. The phone needs to be on or very close to the cradle though, and only supports one phone at a time. It also didn't work when I had my phone on the Qi wireless charger, I guess there's too much interference.
I think they just added this one which is a step up, more gain and supports up to 4 phones:
https://www.wilsonamplifiers.com/weboost-drive-3g-flex-cell-phone-signal-booster-kit-470113/
Thinking of getting a 12" antenna for the Jeep to get that bit of extra signal reach.
Good for the update. It will be interesting to see how well it works on the power line for Spring Fever. Other option is a YAGI as you would be able to point it at a tower.