It probably comes down to personal preference. I wouldn’t say running with open hands will make you tense up as long as your not straining to keep you hands wide open.
You may even find it of benefit to start with open hands and as you get into your running, start to close up your hands if you find it helps you relax more.
video of maurice greene and asafa powell running with open hands.
Not to say jump on the band wagon but don’t write it off. You can always try it out and if it’s not for you then switch back.