My first pistol was a P229 in .40 and it's still my EDC. I've been trying out plastics to replace it, but nothing is matching up yet (the P320 is showing promise, but too early to tell).
First, the M11-A1 is a P229. So just decide if it has features you want, or if it's just marketing. If you can conceal a P226 without issue, do it. I've just never felt the need to go bigger than the P229 myself.
Second, I carry in an MTAC at 4:30-5:00. It is noticeably heavier than a plastic, but with a proper belt it's still fine. The benefit of the weight is a .40 shoots like a 9mm and a 9mm, well not quite a .22, but it's a soft shooting pistol.
The most important thing is learning the initial DA. All too many people shoot a DA/SA at the range by loading, racking and firing. That puts the pistol in SA, and you'll have a very nice trigger pull. But that's not how you'll carry it. So you have to spend the time getting the DA pull down. Decock, fire, decock, fire. Repeat. And keep repeating every range session. One nice thing is you can accomplish this with dry fire. Then be sure to practice the transition from DA to SA. Not so easy to do dry fire.
The nice thing about the classic SIGs is the ability to customize. Change grips, trigger, trigger action (I consider the SRT to be mandatory). And as mentioned, get the Mec-Gar mags. They are the best.
One thing about SIGs is they can be expensive. So try renting and make sure the DA pull is for you. Maybe try one of the .40 police trade ins. My wife actually preferred the .40 P229 to the slightly lighter 9mm P228. If you ever heard .40 was snappy, it's from someone who's never shot it out of a classic SIG. A couple years ago, you could also pick up an SP2022 for under $400, but the cat kinda got out of the bag and the prices jumped up. It's a damned fine pistol, but you lose the plethora of grip options and the SRT option. Still a very nice pistol for the price.
I'll finish by saying I'm not trying to talk you out of the DA/SA, but if you're a striker guy and haven't tried the P320, do so. I haven't had mine long, but it's quickly earning my respect, even though I'm not a huge fan of the grips (Talons help). I got the Carry, and it's virtually the same size as the P229, lighter, and carries 17 in 9mm (as opposed to 15, or even the original 13s).
Good luck!