I've beat them 72 times, it's helped me get about 5 Pokémon to level 100. I've only had the game since last Thursday (9th) not (16th).
I'm currently going to keep using this method. I'm training a Tyranitar right now, it's level 76.
I won't usually use Tyranitar over Wi-Fi unless the other person agrees, because that would be really cheap.
They're easy. But, that's probably because I use 5, Lv. 100's. But Cynthia's Togekiss is the only annoyance for me. My Latias with Thunderbolt or Ice Beam only get's it to red HP and I used a bunch of Stat Boost Items (For Attack, Sp. Attack and Speed).
Well, on to No. 73!