I own multiple cellphone boosters from Wilson Electronics. They have since changed their name to Weboost. I have a few variants of the Sleek. I have two of the Mobile 4G or whatever they are calling it today. The Sleek is the cheapest and probably more than enough for most peoples use. I average an 18db signal strength increase with the Sleek. If your current situation is spotty service, the Sleek should get you to somewhat reliable.
The other booster I own is the Mobile 4G. They call it something else now. It's advertised as a 50db gain with Four devices at one time, each seeing 50db gain. I regularly see 35db gain. Have not seen 50db gain. I only see 35db gain when placing the phone(s) next to the inside antenna. Inside antenna on this model good for upto 5ft of separation from the devices. If it's a work call, place the phone on the inside antenna. Use Bluetooth or wired headset.
They sell "RV" model boosters. These require greater distance between the inside and outside antenna. Advantage is greater interior freedom to move about the RV. I bought the car based boosters. I can move it to my vehicle if necessary.
No cellbooster is magic. There must be some signal to boost. Some cellphone manufacturers respond better to boosters than others. Some cellphone technology performs better with boosters. Verizon 3G service responds well to cellphone boosters. Some people like to upgrade the cellbooster antenna. This helps and hurts. Antennas have tradeoffs. Antennas that work great with 4G service might hurt 3G and 1x. I have found the center of a vehicle hood to be a good consistent spot for the magnet mount cellbooster antenna.