Adapters

They need to be billet, not cast aluminum. Follow the instructions and make sure you check the torque on BOTH sets of lug nuts several times in the first 50-100 miles. Torque to the actual specification, not just armstrong torque. Do all that and they're absolutely fine. Show me a wheel adaptor failure and I'll show you 1-a cast adaptor or 2-improper installation and maintenance.

They need to be close to 1" thick to have enough material to support the second set of studs. Most 14" and 15" wheels will not have enough backspace off the shelf to run an adaptor with anything other than a super skinny tire. Which usually means custom rims for any normal tire width.