SMS - Both are capable products. However, look at product support and that will tell you which way to go. I don't know where you are based and that may affect your choice. I would agree that the MX15 range is easier to control, but I believe you still can't put an MX15 on an MX15i mounting if you needed to due to the MX15i failing. The is due to the CEU being built into the MX15i itself. However, that may have changed since I did my research and may be dependant upon how you mounted the MX15i in the first instance and some form of adaptor may have been produced? With the StarSafire 3, although not as easy to control in the narrower FOV without using Geopointing, upon failures, you can swap out with other SS turrets, including the SSHD which takes the same mounting/wirings. If the info helps.