"LoboGunLeather"
If I may make a few observations:
I feel that rough out surfaces do work on some Inside-The-Pant designs but with the severely shaped and hard molded type that is shown here, I would have to agree with you that it would probably add little in the way of stabilizing this holster. As the purpose of such a finish is to keep things from moving around (not pulling out as that is obviously a function of the clip), with such a limited bearing (contact) surface, I don't think there is much to gain by including it here. That, and I would think again with this body type, contact on the high spots would, over time, burnish down the roughness anyway; making the whole thing moot.
I would assume that you are sticking with a metal clip and it sounds as though you have already picked or designed something that will meet your needs that is of a type other than that shown on the prototypes. If I may add (and you probably already know this), there are heavyweight metal styles out there that can form more of an outward, small diameter "J" at the bottom rather than just the conventional angular "bend" that is usually part of the closer and contact point configuration. That way, if the user chooses to clip the holster to his or her waistband rather than to the belt itself, if there is a belt outboard of the clip, it can be set into the loop (or at least positioned relative to it so as to be caught it if upward movement of the holster does take place on the draw).
At the same time, inward "piercing(s)" can be had either to catch the lower edge of the belt when the clip is worn over one or to press more effectively into the clothing if there isn't one or if it's worn behind the belt as described above. These inward "piercings" (thru the clip body) can usually be designed to create more tension against either the lower edge of the belt (or the clothing itself depending on the application) than is typically generated by what is usually a generally radiused, polished and sometimes plated contact surface in most conventional clips used in this manner.
Clips like this can do some amazing things when compared to what people have come to take for granted when it comes to the traditional belt clips seen for the last century on concealment holsters and pouches.
As to finish, you mention that yours will be flat black. Will this be a powder coating or some sort of applied paint finish? Sadly, most of the finishes used in the past (other than bluing, a nightmare itself in terms of performance) left a lot to be desired in that the flexing of the loop ultimately led to cracking, flaking or chipping. If this is your first venture into such a thing, I'd test the living daylights out of whatever finish you are considering in terms of both this situation and corrosion as well.
The other thing you might want to consider is more than just a "flat" luster generated from the finishing material itself. I realize that it might affect the price, but roughening the surface before applying the finish can (depending on what you are using for a finish) make it truly non-reflecting (as can certain secondary operations done after the finish has been applied). For quite often "flat" finishes (black or not) can still be more eye-catching (for a variety of reason) than one might like.
The only issue here is that whatever might be done to the surface needs to be "done" (as well as selected) carefully so that it does not affect the performance characteristics of the metal itself. You don't want to either work harden (or, conversely, unintentionally soften) the spring. It is possible to do both and just like poor design or improper bending (forming) practices, this can often create overlooked issues that show up at the worst of times. (Sorta the way hydrogen embrittlement issues can mess up otherwise decently formed spring steels when plating them.)
And if I may be so bold, in my experience, a lot of this stuff (from design, to function, to life expectancy, to finish) can be gotten around by injection molding the clip. Really neat surfaces can be created that you just can't form without fracturing metal. Pressure can be created by both design and material. Materials can be found that will stand up better to the "over-opening" many people apply to the clip when putting the holster on and taking it off. And both coloring and mold texturing can employed to provide a surface finish that will look neutral, not reflect anything and not change (or discolor) over time. More and more of these types are becoming available as over-the-counter or OEM parts all the time.
Just a thought.
And one last thing if I may, I fully agree with "Photoman44" and "Sipowicz" that for most (not all) civilian applications, the need to reholster the firearm isn't that great. Now you've got some people who believe they have to be able to do so and that's fine. And you've got other people who actually practice a lot or that will attend schools where they will be expected to reholster after every "run" and they'll need something like this. But generally, "people" (and not the "police") are not faced with situations where de-escalations might force them to put the gun away and employ a different tool or others times where handcuffing and not the gun might ultimately be required.
And looking to one of the real advantages of such a holster (being able to hide guns; especially longer barreled firearms with shorter shirts, sweaters and jackets) you might be defeating the purpose if the pants (waistline) becomes so distended that it, in turn, gives an otherwise undetected firearm away. For if you are dealing with a shorter tube gun (like your J-Frame example here), if this "bulge is problematic and nothing is sticking down past the edge of the covering garment, then you might as well use a tight-to-the-body, Neslon/Askins type design or even a smoothed-out Baker type pancake and not have the problem in the first place.
I might consider an unreinforced mouth version to cut bulk to a minimum and tout the daylights out of that feature in combination with the effect of the clip positioning. And a reinforced mouth version for those who need it or are willing to pay slightly extra for its benefits.
Just a(nother) thought.
And I hope you take all of these thoughts in the spirit in which they are intended. From the photos I've seen here and elsewhere you appear to do good work; with a good eye for detailing. And everybody who comments on your holsters from first had experience seems to like them. And things like this clip location, show good thinking as well. Good luck to you in your efforts.
