From where I see it, ERA and Combat Minion are completely different products, and aimed at different play styles.
Based on the comments so far, Combat Minion allows easier tracking of combat, once you input the OB/DB/Hits of the participants. It handles criticals, initiative, bleeding (I think, not sure on that one), and you can prepare in advance NPCs to use in the combats.
ERA allows character creation, skill resolution, spell casting, combat, foraging, treasure generation.
It obviously has a steeper learning curve, and depending on the house rules of your group, character creation can require more or less tweaking.
The Adventuring module (skill resolution, spells, attacks, etc) works only with characters created with ERA, so you must first make sure to get the values right in the created characters (all skills can be manually edited if required).
There are online tutorial videos on YouTube for both products.
And I'm certain there are users of both in the forums who might provide a less biased answer.
@Jenkyna last time I checked on RPGNow/DriveThruRPG, all ERA RMC modules had 1/5 stars, with no review given and based on only 1 rating. If you think it's nice, could I bother you with a rating? At times I worry that people might pass on trying it because of the bad rating. Thanks!