I think this issue falls into two camps. 1. Those husbands who get nothing to very little at home, 2. Husbands who are bored with what turns out later to be very vanilla sex and want something more. I get that.
I went through looking at what I needed and like you realised that an affair would be too complicated and emotionally draining as theres a good chance of falling for some one. Punting was my solution and its kept things going at home. I dont have sex with the OH but I need to have sex. So as you say its an expensive wank, but its so worth while. And yes you are right, "It is a risk but then so much of life is more fun when there is a risk", providing you don't get caught. Otherwise theres a shit storm waiting for most of us. 
There is a third option which is us men who just don’t find our wives physically attractive any more so don’t want to have sex with them, although to be fair I’ve never seen it mentioned here before so I’d say it’s very rare
