Using a high gain 4G antenna helps you to increase the signal strength, the signal quality and the bandwith of your 4G connection!
Please ask your 4G provider about the frequency which is used for your connection to choose the correct 4G antenna. Most of the european countries (e.g. Austria, Switzerland, Sweden, Uzbekistan, Poland, Norway, Estonia, Denmark, Armenia) use the 2600 MHz band for their 4G/LTE service.
In principal: The higher gain of the 4G antenna (declared in dBi), the higher the range of it.