I would advise them to go to the source because I guarantee that anyone else's imitation ( O'sensei's ) of his lifetime's work will only be an ersatz version, lacking in the real depth of Tom's ( Takeda's ) conception.
(Parenthesis is mine).
I would point out that someone with a teaching license and some different ideas about how to proceed into the future going off on his own is substantively different than someone who doesn't even have yudansha rank "founding" his own style.
Also, if you mean to suggest that Aikido is just watered down Daito Ryu, I would beg to differ. Although the post war growth in Aikido has lead to some important gaps in the transmission Aikido is very different than Daito Ryu. O-Sensei's creation added a whole new dimension to what he had learned in Daito Ryu. If that were not the case, we'd all be better off going back to Daito Ryu. While I actually practice one style of Daito Ryu, it is totally distinct in conception and practice from Aikido. They compliment each other but I would strenuously disagree that one is "better" than the other. But they are truly different.