Not to play the devil's advocate...but,
The issue isn't so much power, or the perceived lack thereof, as it is the internal antenna design and your location on Earth relative to the tower.
Sadly, most cell phones now days do not allow you to connect an external antenna. When fly fishing the backcountry of the Everglades many years ago, carrying the Motorola flip phone, we'd attach a remote antenna to the end of the push pole, hold the pole straight up and instantly had comms from just about anywhere in the backwaters of the park.
The issue is more line of sight to the tower and obstacles between you and the tower; not power. Holding a remote antenna attached to an 18' pole vertically, cleared all obstacles and extended our line of sight to cell towers. Boosters will not overcome geographical and geological pediments to receiving a line of sight signal. Your actual cell comm range will always be slightly less than line of sight propagation; just a matter of physics.
If you have line of sight to a tower your phone should be a to connect without a booster (assuming of course the tower owner is your carrier or has reciprocal agreement).
Also, current atmospherics will either enhance or play havoc with reception/range.
Personally, I wouldn't waste a dime on these boosters. If worried about no cell reception areas, yet needing comms, invest in a InReach device (SatCom). InReach is now owned by Garmin. I've been using one for years and very happy with the performance when in a no cell service area.