I have helped operate a few of these, from the small ones where the guide just attaches to the saw bar to the more precise ones like you show. A friend had one similar to what you show except the bar was horizontal and had a powerhead on each end. Two big Stihls. He had a boat trailer winch rigged to pull the carriage through the log, with pulleys/harness to keep it straight. Worked very well, and let him work it alone.
One thing to know is with the 3/8" width of kerf you produce massive amounts of sawdust. He was putting it everywhere and giving it away as well. Oh and using skip chain with fewer teeth was way easier to keep sharp and it cut just as good.