I have never heard customers complaining about the abysmal performance of the Oracle pseudo-table DUAL. Nor have I ever encountered a real-life performance issue that was attributed to slow access to DUAL. Rarely have I been asked to tune an SQL statement that was sub-second and took a massive 3 consistent gets.
Another reason I won’t be using this tip is that, a few years ago, I did encounter some unexpected, weird, obtuse behaviour in an Oracle system that completely baffled everyone. This was eventually tracked to the presence of not one, but two rows in the DUAL table.
Better to let sleeping dogs lie.