I've got an Arms Unlimited left handed mag release, and it's extremely stiff. It works ok when the mag is empty or only has a few rounds, but any more than 5 and it becomes very difficult to actuate compared to the right side mag button. Even with ten rounds I have to break my grip in order to press down on it at a higher angle with my index finger. On a full mag I have to take my whole hand off to press down with my thumb.

Now obviously the mag will be empty or near empty anyway at almost any time I want to use the mag release, so I can make it work. But I'd really like one that feels more comparable to the button on the right side.

Any suggestions I should look at? Or do I just need to invest in a fully ambi lower? In which case what should I look at?

I like the Troy ambi mag releases.  I have those on all 5 of my lowers.  But that's also the only one I have experience with.  I think they are about $50.

The Norgon is approved by DOD and I was impressed with how sturdy it was, but the Arms Unlimited works the same.  Not sure if it would be any easier for you.  Had the Troy, it worked well but I wasn’t sure about its durability.  Finally just did an ambi lower and went full Nelson when I got the suppressor.

FCD, but sounds like your AU is installed too far. I have one and don't have that problem.

https://www.forwardcontrolsdesign.com/emr-a.html

Surprised no one has mentioned the EMR-A from Forward Controls Design.

https://www.forwardcontrolsdesign.com/emr-a.html

There are other places that sell's them for cheaper, but won't ship as fast as Roger does.

How many turns you screw in the mag release only effects the stiffness of the normal button on the right side of the rifle.

The stiffness of the other spring that actuates the pivoting button on the left side doesn't change in relation to how far in you install it.

Either way, thanks for the recommendations. Both the Troy and the Forward Controls Design look good. I'm also looking at one that Knights Armament makes.

I'll be that guy to say that as a lefty I still prefer running traditional controls on an AR.   I can see their advantage in speed reloads for 3-gun shooting sports but none of the aftermarket lefty side releases so far have me convinced that they give more than their potential liability takes away. They put a fence around the right side mag catch for a reason. True ambi lowers with a properly protected left side catch are a beautiful thing though.

@Duffy

LRF has a fence for EMR-A.  As an aftermarket ambidextrous magazine catch, we haven't figured out a good way to incorporate a fence to it without a complicated design, so we designed the lever to be very low profile, it very likely has the lowest profile than any "pivot on the lever" ambi mag catch designs in the space.  This is done for 2 reasons, one is to make it usable with a TDP spec bolt catch without unduly interfering with it, two is to lower its snag and unintended mag drop likelihood.

EMR-A also comes with a stiffer spring to offset the mechanical advantage afforded by the lever, which also makes the right side magazine button stiffer to push, both things we want.  Production units from 2020 started using the LPD (low profile, duty) shaft which is 1 revolution of the mag catch shorter, so the right side button sits lower on the receiver, below its protective fence.

We paid plenty of attention to unintended/accidental magazine drop risks

New cmmg Ambi mag release is good, and not pricey.