Mildly late to the party but there seems to be some misinformation in this thread, not entirely the poster(s) fault either. A cell signal repeater or cell phone booster takes the outside signal, and then amplifies it. It's not just to take signal from outside and put it inside, you can have the whole system outside, and sit the phone near it and you will get more signal. They work well, rather or not you want one of these over a microcell (commonly misrepresented as a "Cell phone booster") is up to the persons needs. I found this to be an OK comparison, http
/unboxedreviewstoday.com/2016/10/19/att-microcell-vs-cell-phone-booster/
They have some other information on them also it seems.
Basically a microcell can broadcast a signal further depending on the booster used but on average they do, but it's not using legit cell signal, it's just creating a cell signal from the device, which is then routed through your home internet. It's never really using the cell tower at all.
No signal areas could be totally dead and zero signal at all however with signal so close to you it's unlikely, when using a signal repeater or booster you don't use your phones antenna. They generally come with a high gain antenna which can pull signal in much further away than your typical cell phone can. Plus it has the added benefit of being mounted outside, most likely on your roof.
Edit: Got a badge for returning after over a year, who knew lol