My experience with these holsters is that usually, yes, they are tuckable, but with almost every shirt I own the tail would have to be very long in order to stay tucked. With a super-long shirttail, the amount of material that would have to be bunched between the holster and the retaining belt attachment would be a big wad and unworkable.
The only holster I have seen that seems to actually work as tuckable is the expensive Mitch Rosen "Workman" model, which works pretty well because the part that actually connects to the belt is attached to the holster at the muzzle end, giving a generous amount of room to hold shirttail material.
Does anybody know of another holster that is genuinely tuckable, and both conceals a small revolver or auto and stays put? I have owned many that claim tuckability, but in practical use do not function well.
I've carried "tucked" quite a bit in a Comp-tac CTAC (using the standard belt clips). With the belt clips spread out away from the holster body on the "wings" there is a decent amount of room for the tucked shirt tail.
The holster you pictured appears to be a good alternative, too. I like how the belt clip attachment is attached down toward the muzzle end of the holster. It seems like it would be a bit more difficult to "tuck" over a holster that has the belt attachment directly on the holster body, rather than spread apart like a CTAC or MTAC or VMII (with tuckable loops), etc.
Since I can't find my thread about it here on arfcom, I'll post my thread from Kahrtalk
I've got a Desnatis tuckable holster that has a metal J-hook belt attachment that works OK with a Kahr PM9 but I wouldn't try it with anything larger.
Most guys who carry a full size pistol in a tuckable holster with those big kydex belt clips are kidding themselves if they think nobody notices.