If you tried to use the faster technique known for a right X-draw and right straight draw, you'd have a fearsome hard time....Doc's X-draw first technique, where the left side gun (in the X-draw holster) is re-holstered with the left hand by gripping at the top strap as the right hand draws the right side straight holstered gun would be complicated with the flap...basically, the flap is going to close and you'll have to find a way to flip it up and holster the gun with the same hand very quickly, or you're wasting time.
But to each his own. Personally, I believe that if a cavalry man were fortunate enough to get two pistols and were in your shoes, he'd cut the flap off the x-draw holster, but that's just my opinion.