Check what LTE frequency bands are used there by your mobile operator. E.g. here in Finland some places use 800MHz band which is not supported by Mi4 FDD-LTE model so there might not be any advantage to pay extra for it.
There is listed 2 operators in Bangkok and they use band 1 (2100MHz) which is supported by Mi4 FDD-LTE model. Mobile operator web site could have more recent info and map of covered areas.