I have / have had a couple of SH's (Mitch Rosen and Galco) to carry a Government and twin mags. They are not comfy. The draw is slow, reloads are even slower, and you need to accept the fact that you are going to sweep yourself. Tie downs are good things - esp on the offside. IMHO they are best suited to driving gigs or some other special circumstance where they make sense - same for ankle rigs (which I use a lot more than an SH). As a general carry rig - they aren't advisable. For me, I am still faster drawing from a strong side IWB from the driver's seat than with an SH. That said, the draw from IWB is very overt in comparison to an SH. Many moons ago I was behind the curve with a beautiful person at my driver side window (down) and the ability to inconspicuously slide my hand in and thumb the snap for a discreet draw was a distinct advantage.
FWIW & IMHO Design notes - thin straps are more concealable, the wide straps are unnecessary - this isn't a ruck. Softer and thinner leather flexes with the body better and rides more discreetly under a thin cover garment, it is also less prone to squeak. The union of straps in the back is critical - avoid big rivets or anything that is going to create a high spot, as this will be where all the weight is borne and will prove to be uncomfy. Depending on the design (Galco) you may want to use a pair of pliers to bend the snap away from the pistol just a bit so you pop the snap open with pressure of your thumb hitting the snap as you mount the gun (speeds up you draw). Again tie downs are good things. Lastly, work on your draw and reloads at first with an unloaded weapon from a variety of positions - get comfy with the fact you are going to sweep yourself. Get grooved on keeping your finger out of the trigger guard until the muzzle is oriented toward the POA. Once you're confident, then shift to a hot weapon.
