The Mini Fucker is comparable to my own standard Penis Plug from Steelpleasures.co.uk, that is with a diameter of 10mm at its widest. Now I'm not an expert of the male anatomy, and my penis is a standard median 6-inch - and definitely smaller when soft - but I did not have any great problems with insertion and wear. True, I played a bit around first with homemade sounds, pens, thermometers and the like, but was absolutely NOT into any sounding/gradually widening trip. The 10mm PP slipped in with a slight sting and thereafter changed my life. The rush was incredible and stimulated my sex life to a certain degree.
I have written about the following before on this and other PW/PP-threads here (great forum, btw) so this is a repeat:
I wore it for several weeks and was genuinely concerned that it would grow fast, when it suddenly slipped out of itself. This was after a short period of stinging and smarting at the tip - something I now know as a warning that the urethra is about to expel the intruder.
I put it back and had the same experience later: stinging/burning feeling at the pisshole - and now I just pop it out and give my cock a day's rest before replugging. I can now usually go for a few days before I get the signs. It is routine.
I have bought another plug from my dealer steelpleasures, the Socket Plug, which I had specially made at a larger diameter, this time 10,6mm at its fattest. This is an even better plug. but the same thing happens regularly; a slight irritation that signals that I better get it out. If I do not remove it, it will slip out of itself. If this happens in bed, OK, but pissing it out is not a good thing - it costs too much to be flushed away, so when that happened there was some fishing about before i secured it again

I wore the SP for 5 weeks before it came out - after that I could not get any of them back in. It seemed as if there was a ridge or constriction that was not at all elastic as the first time I put the PP in. I wrote about this some weeks ago...
Well, I finally gave up on stretching as I understood the ridge was some kind of scar tissue that would not go away. I would not be denied, however, so I finally got my nerve up and pushed and pressed until <something> broke. There was blood, not the slight red wash that you can get when sounding or pushing, but this was a definite tissue rip. The blood was steady red and had that "bleed" quality that you instantly know. Well, I pushed a little more and the PP slipped in, and stayed.
The blood stopped more or less immediately, as I knew from reading other mails on this forum it would. No pain.
My theory is that a ridge or ring formed inside the urethra outer chamber (where the body of the plug rests - narrowing to a thinner neck behind the pisshole) - this ridge or tissue probably formed as a callus will on a foot or hand being subjected to constant irritation/abrasion. So anyway, I pushed through it and it's gone. No more problem...
My system is now regular: I alternate between the two plugs, after removing the small standard PP I rest for a day and slip the larger Socket plug in. After a few days (less if I have a good fuck which will irritate the urethra) I pull the SP out, rest a day and go back to the PP. (The SP is definitely better for fucking, as the steel ball does not cause pain to my partner's insides, as the pipe from the standard plug (as your Mini Fucker) does.)
To cut this short and answer your question: there is nothing in your cock that will stop you from pushing in a 10mm plug and let it rest inside. The urethra is easily stretchable to this width. Going past 10mm will, as others have stated on the PW thread, take some time, and going beyond 12-13mm is a LONG way off. Of course, not being a doctor, I am judging this by knowing my own standard type cock. Maybe a pisstube only will let a 5-6mm thick instrument in, but I doubt it. I've seen the thickness of doctors' catheter hoses...
Use some good lube, try widening with a artist's brush handle of necessary thickness, a slim Sharpie marker or some such thing, use a salve containing a skin desensitizer, like XYLOCAINE, and get that plug in - damning the sharp pain during the insertion. The rush is absolutely worth the sting.