D151 is a cleaner wax, potentially with fillers. Most cleaner waxes are not designed to be "filling products", but their filling abilities are derived from their abrasives and polishes. D151 offers slight protection because it leaves behind wax. As mentioned probably a million times on the web, D151 is a one step product that doesn't require any additonal coats of wax.
Power Finish is a polish with diminishing abrasives. It does not fill if worked in completely. It does not offer any protection because it does not leave behind a wax like D151 does. But Power Finish has the ability to finish on par with products such as M205 with a white pad, while packing good correction power on ceramic scratch resistant paints.
When purchasing cleaner wax, consider that a jack of all trades is a master of none.