anyone have an opinion on these.

www.blackjackbuffers.com/index.php?main_page=product_info&products_id=357

This?

I have one. It's okay. You can't release mags the old way except with difficulty. You still need two hands to release a magazine because you must hold the gun steady with your support hand while pushing the tab with your strong index finger. In other words, just holding the gun at your shoulder with your strong hand is not enough. It's too heavy to hold while releasing the index finger to push the tab. If you drop the stock to your shoulder pocket then you can do it one handed.

Mags do drop free if you tilt the gun forward a little. It's no faster than using the normal catch with the technique of pushing the release with the fresh magazine.

I think the reason that the countries who have tried to improve on the AK's design, like Finland, Israel, or Poland, haven't incorporated this feature, is because it's not an improvement.