Atom is also used as a generic term for a family of cores mostly used in Atom processors. The present generation of Celerons combine a mix of Atom-based (Bay Trail/Brawell/Airmont/Cherry Trail, etc) and Core-based (Haswell/Broadwell/Skylake) cores.

The J1900 is based on the Bay Trail core, which is a generation-back core also shared with the Atom processors. It's a quad-core, and actually almost decent -- the Bay Trail and newer Atoms are out-of-order CPUs (like Intel's mainstream processors since the Pentium Pro, but unlike the original Pentium and older Atom chips/)

Just depends on the cost vs. performance balance; the J1900 is a great chip if your goal is to put together a sub-$150 new desktop as say, a media player or for embedded use, or as the core of a NAS. It's almost tolerable for light general use.

As chx1975 noted, the Core-based dual-core Celerons are actually halfway decent; I wouldn't buy one in a laptop (in general, I recommend nothing less than a U-series i5), but the newer-generation desktop ones have higher clock rates and are perfectly tolerable for general use.