Explain the "tuckable iwb" please...
There are a number of clips available for these tuckable style holsters.
The standard covers the front of the belt, which is plainly visible but often overlooked by the casual onlooker. To me, just not enough concealment and negates the holster.
The J hooks go up over the pants, behind the belt, and snag the underside of the belt to help keep the holster in place web you draw the gun. Much better in concealment, but doesn't help support the weight of the holster.
The third type, which I use on my tuckable holsters, is the C clip, which functions as the J hook, but has a top piece to ride atop the belt to help distribute the weight of the gun and keep the holster in place. The C clips thereby hook on the top and bottom of the belt, but the front is open, making it less noticeable. The downside is that you have to get the right size for your belt width, or they don't stay in place as well.
I think M-tac still sells all of the clip types, but I haven't seen them available from all holster manufacturers. I just ordered the new clips (in a color of my usual belt) and swapped them out.