The 9mm’s recoil and muzzle flash from a vest-pocket sized pistol can make it problematic to practice with.
Also, that 1.5x1.2x whatever width increase is not something that can be comfortably tucked in a boot or, in the case of my nurse friend, carried on a garter strap. The tiny Rohrbach R9 (which is what I think you’re referring to costs $1149. Out of the range of many people.
I think you forget just how small something like the Baby Browning is. A Baby Browning weighs a mere 9.7 ounces, is only 4.1 inches long and is just 2.8 inches tall.
I didn’t give the width, the DB9 is .8 inches and I think the Browning .25 is wider.