The KM 110R is beefy and about the same as the 90R
The only reason---cheaper to purchase a new carb. 35.00 for the carb and 20 minutes to install. I am not sure about the other line trimmer you choose.
The cost is different as well.
My two 110's and 90's is still going after 4 years of use. The 4-mix units are work horses for light commercial work.