I too kind of got started on this by an adventure with a super-kinky bdsm woman who included some strap-on in her (fantastic) act. My main reaction to the whole strap-on bit of our encounter was mostly "oh christ, this is weird and uncomfortable" but SOMETHING must have ticked me way in the back corners of my unconscious.
It was really a year or two later that this unconscious temptation started to pique my curiosity again. I'd started occasionally nosing around in the trans corers of porn websites - just watching the ladies stroke themselves at first, and gradually getting into everything.
When I finally took a plunge and hooked up with a top gal, it was just kind of freaky, walked away thinking, "What the HELL did I just do???"
But I came back and gradually learned to enjoy it quite a bit.
There's SOMETHING incredibly sexy and arousing about being with a beautiful woman who has a raging hardon coming at you. For one thing, it's the clear evidence that she's AROUSED that's part of the turn-on.
Once one gets used to it, knows how to prepare and all that, getting penetrated by a flesh cock (covered, of course) is rather as pleasurable as doing the penetrating - my experience, anyway.
And to your primary question, getting penetrated by a piece of plastic, rubber, or vegetation (lol) just isn't the same as getting penetrated by flesh. I'd liken it to fucking a doll or fleshlight as compared to fucking a woman.