With the single reel sliding back and forth along with the developer, you could get surge streaks around the sprocket holes, or effectively less aggitation (due to the film moving with the developer), or something in between these extremes. But, the effect is likely to be inconsistent between rolls.
Get the second reel, put the empty one on top, fill the tank, and your consistency will improve.
For 35mm reels, I strongly recommend the Hewes reels, which have cleats to grab the sprocket holes, rather than the center clip. They make loading far easier.