Hi Adam
Digital pH meters are excellent for liquids but are unlikely to give an accuarate reading for carpets because there is not enough liquid.
So to test the pH of your solution they are much more accurate than papers but to test the actual carpet they are not.
pH athough important, is not so much so that you need to know it to 0.1 say, papers are accurate to about 0.5 which gives a good indication.
Cheers
Doug