I have the BAD lever. Here's my honest opinion. I like it. Not so much for reloads, because when you insert a magazine with your non-dominant hand, it's in a position to hit the ping pong paddle already. However, on a double feed or malfunction, it's stupid simple to lock the bolt back with only one hand.
I have found however, that sometimes when ejecting a magazine, I would accidentally hit the BAD lever, and send the bolt home on an empty magazine, requiring me to manually charge the handle on a new magazine. I have only done this twice out of a few hundred magazine changes. My friend shot my AR, and had the same issue. It's not enough of an issue for me and what I do, but for others it could be an issue.
Also, it takes up space in the trigger guard and I can see a potential issue for someone wearing large winter gloves.
The BAD lever itself feels solid, and performs as advertised. I am keeping mine on my AR.
If you're concerned about creating 'training scars' by becoming reliant on the BAD lever, I would practice with and without it, as you can still use the AR as was originally intended, even with the BAD lever still attached.
That's my take on it. Hope it helps.