I don't know what sort of rust inhibitors it has, it may be fine. The reason we use after run oil in glow engines is that methanol is hydro something or other (technical term, hydroscopic maybe) and attracts moisture that causes bearings to rust and your favorite bearing supply company to smile. If you run an engine say weekly you'd prolly never need to run after run oil through it but let one sit up for a month or two without it and you may not feel the roughness but tiny pits begin to develop in the ball bearings six months and you will feel the roughness is noticeable, a year and the engine may be hard to turn over or not do so. The stuff is cheap insurance and easier to apply than new bearings. Two strokes aren't too bad but four strokes are a PITA don't ask how I know so much about this.