I've seen a number of negative references to the P290 slide thickness around the Net. I think that it is a matter of perception, due to the pistol's overall small size, rather than reality. Here is a comparison of some widths:
P290: .9 inches (1.1 inches w/slide catch lever)
Glock: 1.18 inches
Nano: .9 inches
Shield: .95 inches
PPS: .91 inches without slide catch lever, 1.04 inches with.