I spent well over a year working on the Offset Belt Clip IWB model. Early in the development work I found that the belt clip itself was very important in optimizing holster performance. None of the clips available from my suppliers provided either the required strength or design (contour, dimensions, etc).
I contracted with a manufacturer to make clips to my specifications, sent payment, and was given a production date. That date passed without performance, then I was given another production date. That date passed, and they stopped responding to e-mails or phone calls.
Several months later I located a manufacturer that actually produced what I wanted. Clips made of tempered (spring) steel with positive lip to lock on the belt, opening sized to accept most standard trouser belts plus the trouser waistband material and still grip securely (actual opening size 1.70" X 0.25", which works nicely with just about any thickness of belts widths of 1.5" or 1.25"). That manufacturer has proven reliable on several repeat orders and we continue to deliver several hundred of these holsters every year.
Offsetting the belt clip away from the bulkier parts of the handgun (semi-auto slide, revolver cylinder) effectively reduces the bulk of the holstered handgun. This also reduces the tendencies of the clip to snag on clothing, furniture or auto upholstery, etc.
One downside remains, which deserves mention. Offsetting the belt clip makes the weight of the handgun less stable. The larger and heavier handguns are more likely to shift in position during normal activities. For this reason I offer this holster model only for the small to medium (size and weight) handguns.
Everything in holster design involves compromises among the 4 basic factors of comfort, accessibility, security, and concealability. Whenever one factor is emphasized there will be compromises among the other factors. There is no perfect holster for every user or circumstances.
IWB-style holsters emphasize concealability by keeping the bulk of the holstered handgun inside the trousers. The compromises come in reduced accessibility (both in ease of draw and ease of reholstering) and in comfort (many people simply cannot tolerate the bulk of a holstered handgun tucked into the waistband).
With IWB carry the overall size of the handgun makes a great deal of difference. Enough of the handgun must be contained within the holster to provide reasonable security (retention) and the weight and weight distribution (including ammunition load) have to be low enough for the belt to stabilize the holster. The smaller and shorter the handgun is the more accessibility will be compromised. Probably the worst IWB candidates are the subcompact polymer-frames large-capacity semi-autos; but those are exactly the handguns that many people wish to carry in this manner.