I've just had a 16'x14' section of concrete poured adjacent to an existing 30'x14' section of cement that was stained by the previous owner. I would like to stain the concrete to all match. I see there are paint/stain removers on the market but the reviews are mixed on the products I've looked at. Anyone here have experience with this and any advice?

Is the stain mixed in the concrete or applied on top of concrete? If mixed in concrete that is your color and you'll have to match new slab to old slab color.
You can try an acid wash to try and remove if stain was applied on top. Results may not be consistent.
Acid wash the stained slab than go with a darker stain on both to match.
I'm not a fan of stain over concrete over time it shows traffic wear patterns and chair/furniture marks.
Good luck,

Skim coate over both and then acid stain what ever color you choose so they both match.

I used Colors Direct and did it myself, they have everything you need to do it.

I would do a "test" in a small area before doing the entire surface. Make sure it's going to match to your liking first.

Thanks all for sharing experience and advice!