The new $429 iPhone SE and $599 iPad Air with 5G connectivity do not appear to support the fastest mmWave 5G bands, based on the technical specifications listed on Apple's website.
Both the iPhone SE and the iPad Air mention support for the following 5G bands in the U.S.: 5G NR (Bands n1, n2, n3, n5, n7, n8, n12, n20, n25, n28, n29, n30, n38, n40, n41, n48, n66, n71, n77, n78, n79), but there is no listing for mmWave bands as there is for the iPhone 13 models that do support faster 5G technology.
With no support for mmWave 5G speeds, the iPhone SE models will be limited to sub-6GHz 5G. sub-6GHz 5G is still faster than LTE in most cases, but it is not the super fast impressive 5G speed that you see in marketing materials.
Sub-6GHz 5G is much more widespread and will be the 5G available in rural and suburban areas, as mmWave 5G is shorter range and limited to more urban spots. That said, AT&T and Version have been expanding their faster 5G networks drastically in the U.S. with the release of C-band spectrum, and it is not clear if the new iPhone SE models will be compatible with the higher speed 5G available from the carriers.
The iPhone SE 5G and the iPad Air will be available for preorder this Friday and will launch on March 18.