The thing you need to consider is the presence of other 2.4Ghz devices operating in your immediate vicinity (including that of a neighbor in an adjacent apartment): cordless phones, wireless cameras, routers, etc. I was trying to figure out why my mobile router wouldn't work well in my car when driving, only to remember the back-up camera I installed months ago....
In fact, even a mobile wi-fi router (e.g. Cradlepoint PHS300) operating at 2.4Ghz can interfere with the reception of a 4G modem (2.5GHz) that is plugged into it, killing bandwidth speeds. Hence the suggestion to use a 10" shielded USB extension cord, when using a 4G modem with a mobile router.
Realize that many users are spoiled by using a 3G modem along with the same mobile router being used with a 4G modem (I even had my Sierra Wireless 597 Compass 3G modem velcroed to the SIDE of my PHS300, a bad idea for a 4G modem!), where interference between a 3G modem and it's router wasn't as much of an issue as with a 4G modem.
Just saying, we're immersed in a sea of electromagnetic fields, and interference between electronic devices is an increasing concern threatening performance of both wi-fi systems and 4G.