The only problem if you use eastsheen for speedcubing is that you may not use them in official competition. Notice how I said "official" meaning a competition where the rubik's company SevenTowns is incorperated.
Where did you learn this? This wasn't the case at the 2003 world competition. I used the rubik's 5x5x5, but many others used the eastsheen version. There were also eastsheen 4x4x4's. For the 3x3x3's, I think they only required that it had a rubik's logo.