hi, if your house (place of using) is completely blind of any 4G signal (not 4G coverage area now), 4G really only available 3km away, then using high gain 4G antenna would help only IF YOUR 4G MODEM/EQUIPMENT IS NOT END USER CATEGORY, means not these personal usb modem, MIFI as their built in wireless power is moderate only. Industrial type amplifier gadgets will help.

For using personal usb modem, MIFI, if seeing very weak 4G signal (e.g. -90dbm, -100dbm), at least got seeing the 4G network, or can see 4G network but cannot register to it, or sometime appear sometimes gone, connected but line unstable, etc,  then can go for high gain LTE antenna as solution.