[Robert Harvey]

I used a set of eBay cheapo external ones to monitor a suspected slow puncture on my Audi, worked fine, but they do weigh 8gm each so in theory slightly unbalance the wheel.
My local place balances to 5gm which they say is good for 150mph, and I haven't noticed any symptoms of imbalance. Since they were temporary I didn't feel like paying for rebalancing