I have not played the game myself, however, I have played a lot of similar games. Such items like 'Boots of Flight' (an example) that increase speed by five, or a 'Bow of Hunting' (another example by me) that increases Range bonus' by a certain amount should not require you to use more than one. Rather, they should increase the total by the number provided.
I would wait until Ravager or Fljotsdale answers this one, however. Both reside in the English timezone, and it is 2 o'clock AM there. I'll mention this in passing if I see either of them online, though.
