ATB,
I already have the metal ball links. I think they're 3.8mm and they were $15 from Helihobby. I bought them during the blade grip shortage because I was desperate to get back in the air. I made that modification on one broken grip and used it temporarily until I could get new grips. The metal-balled grips are stronger without question. The reason I changed it back out to plastic-balled grips is the same reason I never went to CNC grips like many others during the shortage. The grips act as a fuse or shear-pin. When they break they saves parts further up the line, and since they're cheap and easy to replace I decided to stick with them. The crash I had was into the stairs of a deck and the damage was minimal. I believe this is largely due to the sacrificial grips.

Strat this is a killer mod, you'll really like it.