This week I started using a toggle retention for my wide grip slings. Now I am used to it and it feels great.
Can definitely recommend it !

I've made two, one that was really short and made of cotton string and reindeer antler, the other super long and made of jute and buffalo horn :D I took the short one apart and I've been meaning to reuse the handle for a new longer sling. The long one is a lot of fun; I should break it out again.

Any good pictures out there for the setup of this?  I've done a couple searches but not finding anything yet.

Mine is really simple. I use a round piece of hardwood. About 3 cm in diameter. I cut a notch all around it with a siwss army knife, the notch located about 2/3rds on one side. Then I tie the retention loop around it with a good cinching knot that doesn't let go.
I exit the retention cord between pinkie and ring finger. Or flip the toggle around and the cord exits between middle and ring finger for less cord seperation. The exit is a little higher up on the fingers then a fingerloop that would exit from the base. The toggle is held by 3 fingers, the pinkie, ring and middle finger and is not larger than it needs to be.  My index and thumb grip a small flat release node at the end of the release cord. This gives quite a hair trigger. 3 fingers retain, 2 fingers release. 
it somehow feelas as if the toggle is also beneficial for getting the wrist orientation right. Its dark now so no picture atm

Another feature I’ve tested but years ago.
You really have a habit of switching slings J
I’ve alway liked the idea of a toggle because some of the slings in baldurs gate were shown like this .
From memory I didn’t hate it I just prefer a cinching fingerloop.

Edit
Here’s a pic
Looks like some sort of release aid is on it too.

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You said ''You really have a habit of switching slings J ''.

It all stems from a fight in my head, between the wide grip and the tight grip. The vast amount of sling types I experiment with follow out of that.  it also stems from a fight between two projectile types, the elongated one and the sphere.

The cotton one, like I said no longer exists, but the jute one is still in great condition. It's good to look back at old stuff because these slings look so ugly to me now :D

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I’d say that the cotton one looks kinda ugly but the jute one doesn’t look so bad.

I never used to taper my release cords because I just didn't really think to so yeah it's not great :D The jute one I would make differently nowadays. I would make the cords thicker, the pouch I would add extra material too and I would taper that release.

They both look like nice tight and even braids to me.

I've seen toggle release mentioned a few times, but never really knew what it was until now.  This will need to be added to the thousand other things I need to try.

It's really simple, put a stick through your loop.
It's great for wide grip but can also be used for tight grip (cords inside the hand)
Still thinking of an easy way to make it for a tight grip.
I remember Techstuff did it.
I am specifically also looking for a way to get a ''relax trigger''.
To take all the load of the releasing fingers and release with the simple tap or press of finger,
but in a way that doesn't utilize modern archery triggers. I think this can be great for accuracy, especially
when combined with a Y-sling (my favorite type, the only problem I have currently is that I need
to grip the release cord of my Y slings extra tight because the release cord also carries 2/3rds of the retaining power and this
hard tight grip doesn't allow my hand to relax. I either need to use a very big release node that is detrimental to accuracy
or use a full fist grip with these slings, which also does not give the cleanest hair trigger )
A conventional sling could also benefit from such a relax trigger system, of course.

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