Matches, There has been quite a bit written on small of the back holsters. They are a great idea but tend to fall short in execution. Putting a large piece of steel against your spine tends to increase the risk of damage to that critical body part. Issue is if you fall on your back, which is likely to happen in a fight. and can happen occasionally when you're not fighting, the gun can cause damage or even a fracture the vertibrate. There is very little padding over the spine at this point, reach back and check.
Second issue for me is the draw. When you draw out of an SOB holster, you really don't have control of the muzzle until it breaks around the side of the body. I have an issue with this as in a stressful situation, if you prematurely break the shot, you have no idea where it is going. With some poorly designed SOB holsters, you actually have to sweep the muzzle across your mid-section during the draw. This can cause really bad things to happen.
Finally, SOB holsters are the most uncomfortable things in the world for every day wear. They are ok if all you do is stand or walk around but if you spend any time in a car, go to dinner, sit and watch a movie, or do anything else that requires sitting on a chair with a back, you will very quickly loose the feeling in your legs from the gun pressing on the nerves. This puts you in the situation of either having to remove the gun from the holster (not always practical), or fidgiting like a prostitute in Church (not a pretty picture).
My advice...find a good strong side owb or iwb and stick with it. And of course, practice getting the gun into action from the holster.
Hope this helps, of course it is just my opinion...