Every time I've asked someone from S&W whether any LE agency has ordered revolvers (like J-frames) made without the ILS, I've been told no, that they get the same revolvers the public buys.
The Model 40/42 doesn't have the ILS, BTW.
None of the cops in the DAO J-frame revolver armorer class I attended had anything bad to report about the new style revolvers equipped with the ILS, used by either themselves or any of their folks. Granted, a couple of other guys who had also apparently used revolvers as service weapons back in the day didn't seem to care for the ILS for cosmetic reasons.
I asked the instructor if any other armorers attending his classes had reported functioning problems related to the ILS and he said that it hadn't yet come up as something which had caused anyone problems. (And J-frames are very popular as off-duty and secondary/backup weapons.)
Only one of my J-frames has the ILS, a M&P 340 (because it wasn't available without one). I've had no problems with mine, and it's actually carried more often than my pair of 642-1's or my 649 Bodyguard (older .38 Spl model).
I've handled and fired a number of ILS-equipped S&W revolvers, and have also observed other folks shooting them, as well (and have helped maintain some for other folks who own and carry them as an armorer). No problems experienced or observed to date.
Given my druthers I'd prefer a revolver without the ILS, since I use other methods to deny unauthorized persons access to my weapons, but that's just a personal preference. I have been thinking about adding yet another J-frame to my collection of retirement guns. A M40 nickel or M42 Airweight are currently at the top of my list in that regard.
My M&P 340 is a fine shooting little gun, though.