This is a very good debatable subject actually. I know several woman who use their "bobs" on a rather regular basis due to either having a very high sex drive, or they simply aren't satisfied sexually. However, very few of them are in serious relationships, and the ones that do enter a relationship, tend to let the "bobs" get dusty. (unless they use them together-playfully)
But , it just strikes me as sorta double standard, most men are quite fine with their ladies using them, but it seems when the tables are turned, women(not all) think of it as perverted, or just plain wrong or as though they just aren't enough to sexually please their partner and in turn, feel as though their man isn't being altogether faithful.
I think that device is meant for men who are having issues getting a partner, and if they had a partner I could see them getting a tad bit miffed ( or quite a lot) about not "being enough". It'd be one thing if he had such a high sex drive that he lets his partner get some rest, but something all together different if they preferred that over being with their partner.
And I would only classify that as "cheating" if he wasn't honest about it, like sneaking off and playing on it , hiding his true intentions, denying her sex just to ejaculate elsewhere to someone else's image. And frankly, I'm not comfortable labeling it as cheating, but there's certainly a note of betrayal attached to that.
And a whole 'nother issue arises as well, there are some who are addicted to porn , and I can only see it escalate with such a device.