The LM2576 is a DC-DC converter. If you use it between DC-DC and MCU you have two DC-DC converters in series.
Efficiency:
* The efficiency decreases when connecting DC-DC converters in series.
* it depends on your MCU current consumption and voltage difference. If it is only a few mA and you step down from 5V to 3.3V then a linear regulator (LDO) is usually the better choice.
In a larger assembly, using an isolated DC-DC converter
may not give you isolated equipment; every path to earth
ground must also be isolated (signals, other "grounds", etc.).
But is isolation what you want to be "effective", or some
other aspect(s)?