I have a CTAC for my M&P9 and it conceals the full size pretty darn good. And I'm not a big guy either. Obviously I couldn't do it wearing shorts and a t-shirt but if combined with proper carrying attire you'll be good to go.
However, I'd also recommend you look at the Milt Sparks Versa Max II. It is expensive and it might take some time to get one but they are fantastic and more comfortable than anything else I've tried. I used to carry a full size 1911 in one every day and barely noticed the size and weight.
There are really no wrong choices from the custom makers. That said, thinner conceals better than fatter - and thinner 'usually' means kydex. Leather IWB's which have the belt loops offset from the body of the holster are also very concealable.
Comp Tac is universally loved, BearClaw Holsters has very streamlined designs and is top-shelf, and Dan Hillsman is also worth mentioning as a top-notch custom kydex maker. Examples of the offset belt loop IWB would be the Southern Holsters 'Memphis', K&D IWB Defender, or the Sparks VMII.
m4arc -- As chooch said, Rick @ CCC made the holster to my requested specifications but really it was not rocket science on my part. He did the actual design and made it work. I'm sure if you tell him you're interested in one, he can knock it out for you in no time. The entire holster (body, belt clip, and shirt guard) is made from a single continuous piece of kydex. There's nothing to break or come loose. The only change I'd recommend is that the shirt guard is a little too big and might interfere with getting a perfect grip in the holster; I'm going to shave a little material off mine where it meets the beavertail and back of the grip. Rick offered to make any changes but this is just too minor to bother him with, and I don't want to be without the holster.
As for the knife, S&W gave it to me for telling people not to worry about the mag drop issue.
I won it at the S&W Winter Championship earlier this year. It's a first production run so I'll probably never actually use it, but it makes a good photo prop.
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