Strap on? With a guy, no.
Wanting the experience of fucking me with a bigger cock speaks of a man who is very insecure about his size and how that relates to his performance that, were I in a relationship with him, I'd want to help him be happy about what he had instead of grunting and moaning on the end of a fake cock and possibly making him feel worse.
If I weren't in a relationship with him I don't quite know how I'd respond to a request like that. I'd want to decline but I don't know whether it'd change my mind about having sex with him at all.
A lot of people post good experiences about penis extenders, but I kind of feel the same about those.
I guess mainly I think that if a man wanted to "use one for your benefit and his" I wouldn't think of the 'my benefit' part - because I wouldn't need it, or want it - so it would only be for his benefit and I don't think that would necessarily benefit him in the long run.