Hey man! We meet again. So I can tell you from experience that the experience is probably 2/3 of what you might get from smoking/vaporizing in terms of absolute bioavailability. There is going to be a noticeable difference in terms of the rush or the time to onset of effects that you would have to get used to, which I think would be the most significant difference to the average user.
There isn't nearly as much information out there regarding rectal Heroin as there is regarding rectal Morphine for obvious reasons. I think that being that Morphine and Heroin are so closely related chemically and that from my own experiecne that the 2/3 ratio is good enough to use as a benchmark.