Just do a compression test to check for binding. I adapted my ofna 1/8 ultra bones to my 2wd stampede. Was great for the first week. Some jumps and cartwheels lefts them curved.
Hpi uses them to cushion the dog bones and cvds in the metal drive cups. Think of it as foam peanuts in a package. All of my Nitro Rs4s have them installed. I think my cen f450 does too.