As far as I know, the main benefit of Manuka honey is its anti-bacterial property, for bacterial infections in mouth, throat, and maybe upper GI. It can also be applied directly to things like leg ulcers where there are claims its anti-bacterial properties help with healing. If bacteria is not your issue, then no point paying for Manuka. All honey also has some anti-inflammatory benefits.
I have used Manuka with a sore throat, but of course I can't tell if it was due to a bacterial infection, or if the Manuka honey made it heal faster, as sore throats do normally heal anyway if you do nothing. (Strerilising your toothbrush is also important if you have a bacterial sore throat, so you don't keep reinfecting.)