I have lots of K12 customers using metal protective cages in gymnasiums, pretty much without issue. Without getting into all the theory of Faraday cages, the spacing of the bars of the cage compared to the wavelengths of 2.4 and 5 GHz signals... I'll just say that in theory, there's a small impact, and you're better off using a non-metal mesh cage for that purpose. Although I've seen deployments with metal mesh cages work "just fine" (customer's description), there are better options.
I'll message you privately, and cannot recommend one 3rd party vendor over another, but can share a couple of examples. There are also certain registered Cisco solution partners who have tested and certified specific solutions with both Aironet and Meraki APs.