Metformin ER vs metformin

Doc just changed me to Metformin Er from regular metformin. So far no issues. I have been on metformin 850 3x a day(2550 total) for years. I am now taking 500 X4
(2000). I am worried that it will not as effective as the straight metformin.
Doc made the changes because I confessed that i forgot to take lunch day pill often.
Any experiences with this?

I’ve been on Metformin ER ever since diagnosis. I don’t find any problems, except that straight Metformin causes me stomach problems.