The cost of fuel is stated as one primary reason that so many modelers are switching from glow to gas. OS has every reason to offer engines that use less expensive fuel, as they do in Europe. The OP says that two brand new OS engines make an inconsistent metallic rattle while running and at the same time give every indication that they are running rich. Do you have another suggestion as to the cause?
OS makes piles of gasoline engines. The people who want to use cheaper fuels use gasoline engines. Glow fuel at $15-40 per gallon depending on locale or $3-7 per gallon for gasoline depending on locale and oil used. Not a complicated idea to grasp the concept of. A metallic rattle to one person may only be a peaked out mixture setting to another. Maybe it's the muffler. It's not uncommon for muffler baffles to be loose, so there's another possibility.