I have sailed and owned boats with mid boom sheets and never saw one I liked for sail control. It's too Winnabago and not within easy reach of the helmsman which is a safety issue in my style of sailing. Dumping the main needs to be done in a split second . I can sail my Ariel with one hand on the Lewmar cranking in the jib and the other on the mainsheet while steering with my knees against the tiller.
What is worse, is when the boom is short and the sheet is on the end in mid-cockpit in front of the helm, now that is a real mess. Mid boom and mid cocpit sheeting are ok for serious crewed race boats that are never cruised or single handed, IMHO .
I was sailing today on a friends Ranger 37, full blown race boat with tracks everywhere and 14 winches and it has a mid boom sheet, a nice Harken system that works well , but it requires a person always within reach of the controls and the helm is not even close when standing in front of the wheel, you are still 3 steps from the sheet .