As someone who is into enemas using a long colon tube, estim, and some other more invasive forms of medplay I must just say use common sense.
If it feels good that dosn't say it is not dangerous.
If you just feel you must try something research it first and know what you should not do.
And always have someone else there to ring the alarm bells if something does go wrong.
If you are questioning your safety, the expertise of the person you are playing with, your gut intuition says no, others are telling you no that do know what they are talking about, if the risk for something going wrong and causing great injury and serious complications, potentially deadly is a possibility, then it may be something you should not be doing. I definitely agree with jansatin.
Yes, some will argue their is risk with everything, that we don't get out of this life without dying. Both statements are true. Doing something because it may feel goo or their is an interest in it where the risks are to high is stupid, irresponsible, irrational.
...Just my humble opinion...
Play safe, sane and consensual.