I like combo bits. That said, I make my own because A) I don't usually need a thin twisted wire bit and B) O-rings (loose rings) need to be fitted bigger than most bits and they usually only come in 5".
Looserings really do pinch the corner of the mouth, so even though my mare fits in a 5", she needs a 5 1/2" loosering in order to get the joint away from her lips.
And remember that looserings can easily be pulled through the sides of the mouth, which means you need to adjust them tighter than with a normal bit, which puts increased pressure on the poll and lips.
I prefer a 6" frenchlink loosering adjusted as low enough that there's no pressure on the lips.
After that I just grab a western leather curb strap and buckle it onto the bit over the nose. Works just the same as a storebought one.