Cat's Eyes are made with rubber tubing, Crossfires are made with steel braided tubing.
Cat's Eyes will tell you if a tire is underinflated, Crossfires will tell you if a tire is underinflated or overinflated.
Crossfires can be found on eBay every once in a while for about $50 a piece. To do an entire tractor, you will have to buy 4 of them (one for each tandem)