You're in the same boat as me, it seems. I am a LEO on a department with a fairly restrictive 'approved list' of off-duty/backup weapons. Basically, anything by S&W is allowed, as long as it shoots .45, 9mm or .38 spl. A few other brands and rounds are allowed (.357, .380, .32 and .25), but thats about it.
Off-duty I carry either my duty cannon, the 4506-1 or my Sig-Sauer P232 in .380. I'm very happy with the Sig. VERY happy.
As an on-duty backup I have a S&W 642- a J frame .357 with enclosed hammer. I like it as well.
Why different guns for off-duty and backup? Because they serve different purposes. The J-frame is a no-frills pocket cannon. Nothing to snag, a one-finger malfunction drill, and plenty of power. Only 5 shots, though, and accuracy is iffy, but this is a backup gun. If I'm pulling it, something has gone extremely wrong and probably gone wrong very close to me indeed. I consider it the ideal backup gun.
On the other hand the Sig is accurate, ergonomic, powerful enough (though admittedly on the low end) and carries more rounds and reloads quicker.
Naturally, they can be swapped at need.
Why not a S&W auto that will take the 4506's mags? I considered it, but in the end, I cannot stand S&W autos. Their ergonomic engineers were on drugs and using crayons when they designed the standard semi-auto grip/frame style. If you like the Beretta's style, you might consider that option.
FWIW,
Mike
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"A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." -Robert Heinlein