I wonder if there is a similar app for the R2? In any case the "LTE Discovery" app on my R2 shows signals only on bands 2, 4, and 13 which implies I don't have band 5 here. I'm getting 5-10 Mbps here anyways - over 50 Mbps in Boston !
I've played around with this, some more, and I think I've learned a few things:
The various "Engineer Mode" apps don't actually create an Engineer Mode. They merely provide access to the phone's Engineer Mode if one already exists.
I've been experimenting with various phones in my "fleet" and go to Settings>Apps>All Apps then tap the three-dot menu and select "show system apps". I then scan down the list of running apps and look for one called EngineerMode. If EngineerMode is present I have been able to access it with an MTK app, even when it wasn't a Mediatek processor. And if I can access it, then I can deselect unwanted LTE bands.
I don't have a ZTE R2 but, from what I've read, it does not have an Engineer Mode.
I also found that my Verizon Prepaid Moto E4 phones don't have Engineer Mode.
Obviously, the ZTE Blade A7 Prime does. So does the LG X Charge.
I'd be interested to see what other people find with their phones.
Check to see if you have a system app called EngineerMode.
Try to access it with an app from the Play Store or by dialing ##3646633##
See of you can access the LTE bands by tapping BandMode>SIM1
Moto G4 Play-- mmfacemm's suggestion gives me access.. Path Data Settings/ LTE/Bands gives access to disable particular bands, and a menu to set priority among enabled bands. (I like this better than entirely disabling bands, since they might be needed somewhere else....)
There is no system app named something like Engineering Mode, though.