I've switched from reg Metformin to the SR (Slow Release) form. It is not called Glumetza though.
The reason for the switch was headaches 24/7. Sugars were fine, except for fasting sugars.
I must say fasting sugars have always been my main problem. Many T2s have problems with fasting sugars.
As far as weight I did experience a loss at the beginning (10 pounds perhaps) but Metformin gave me a hard time the first two weeks so... of course I lost weight because I spent all that time kneeling in front of the white porcelain.
Although Metformin has that effect on some people it is not meant as a weight loss medication. I find the Slow Release form does a great job at keeping sugars stable throughout most of the day. That stability does help though when it comes to dieting.
The very best to you!