Sturdy & stout - Strike Industries Dual Folding Adapter Stabilizer

This Dual-Folding brace is excellent. The operation is smooth and snag-free. Press the button (opposite whichever side you are folding) and it swings closed and locks into place.
To deploy the brace- lift near the hinge and swing out. It will positively lock into place in the extended orientation.
Be sure to use the rubber insert stickers for wobble elimination. I used the 1.4mm bumpers, but they also come in 1.3, 1.2, and 1.1mm.
One caveat- do not over tighten the picatinny bolts as this will cause the operation to be stiff and that could be problematic in a rushed situation. Tighten until snug, then another quarter turn. ~25 inch lbs.

If you have a forward assist on your AR, this will impede the folding operation to the right (in a right handed setup) Not a deal breaker, but save yourself the $ and get a single-folder if you plan on using it on a dedicated AR platform with forward assist.

Another caveat- if mounting on an sig platform- I recommend using the lower 2 slots on the pic rail. This will make sure your fingers do not contact the hinge when using the charging handle. It can certainly be used on the top 2 rail slots, but I found my fingers/bottom of the charging handle would forcibly impact the folding buttons during operation, as opposed to the sig brace, as the joint is slightly lower profile. Just a thought.