I too was wondering about a stitch regulator like the Quilter's Cruise Control or the Sure Stitch Stitch Regulator. When I looked at a video by Leah Day (free motion quilting whiz) she didn't recommend using one, she recommended practice, practice, practice!
But it sounds appealing that the gizmo would help with stitch length, so any comments from those who know, have tried or found out it wasn't helpful would be appreciated by me and maybe some others.
As for tension, I just read somewhere that too much pressure on the sandwich can create problems - I never thought of that as a possible cause.