I've been using S&W 3rd gen aluminum framed pistols for over a decade. I've had alot of contact with other high volume shooters who use them and local agencies who do so as well. I've yet to encounter a "cracked frame problem" on an aluminum 3rd gen. In fact I've only seen two. One of which I own.
Thats not to say it doesn't or can't happen. With enough carelessness or abuse you can destroy any handgun. Even steel ones.
I seem to recall around 8 or 9 years ago that there was a report from a Tennessee LE agency, probably the Memphis PD, that they had destroyed some 40 caliber S&W 3rd gen aluminum framed full size guns. IIRC the details of the "problem" involved inadequate maintenance. IE, not changing recoil springs regularly and no grease or proper lube used.
If you don't change the recoil springs in the aluminum framed 3rd gen guns and don't use grease on the rails (oil does not adhere to the aluminum frames adequately) you WILL have accelerated wear and MAY crack a frame.
Back when I was somewhat lax about my semi auto maintenance and ignorant of factors in prolonging the service life of a pistol I shot several thousand - yes, more than 6000 actual rounds

- through a "value line" model 910 pistol. Almost no lube, changed the recoil spring one I think. At well over the 12,000 round mark and only because it was feeding "slow". I went to right around the 20,000 rounds mark on that gun before I cracked the frame. Gun still functions - but it is cracked and not worth repairing.
So, get a 4043. Buy it, shoot it, love it. And by loving it I mean take care of it too. A $6 tube of TW25b grease and a fistfull of recoil springs costing maybe $15 from S&W will assure you of a long and happy relationship with the 4043 pistol. My 0.02 Regards 18DAI