Those dipstick oil removal pumps are the common method for oil changes.
We share the same concern for the effectiveness of draining of the oil sump.
My over-the-top solution was instead to design and install a high volume / high capacity five-zone oil change system, one for each engine, each transmission and the generator.
Mine sucks out eight quarts in ten seconds, for a five minute oil change. Mine handles oil at operating temperature, so I change the oil after having fun w/ the boat for the day. Mine has bronze gears. If a pump w/ rubber and plastic is selected, then ensure that the temperature limits for those parts are not exceeded.
Mine is plumbed into the oil pan, by replacing the sump drain plug w/ a banjo bolt to the tubing, valves and pump.
Even if the dipstick method is used, an engine has many puddles of oil that don't fully drain into the sump, so even if the sump is fully drained, once the engine is started that old oil will contaminate the new. That is not a problem, because the fresh oil, w/ fresh additives and w/o contamination is the large majority, even if those old drops change the color from clear / golden to darker.
The best option is appropriate / frequent oil changes, at-least as often as specified by the manufacturer. Once an oil change system is on-hand then that is all possible.
Yes, the Gunk Motor Flush won't fully drain, so some of that "kerosene" will remain w/ the new / fresh oil and isn't a great choice. Frequent oil changes are better.