I dunno how a threesome would work for me. I have some strangely monogamous tendencies, so in order to truly enjoy the company of a woman I haven't seen before, it has to have been a while since the last woman.
That being the case, it's just not something on my horizon. I'd rather just book the one lady for longer.
A threesome *could* potentially work for me with two ladies I've seen and who know each other well; but I won't go out of my way to make something like that happen.