The 'tumors' were supposed to be a reference to leather bags he had stored in his legs. Was actually planning to move those to his lower abdominal cavity and [possibly, now certainly] remove the reference.
And, obviously, the bags would have various drugs/food items in them - Except one that just had an empty bag in it for future usage.
My thought on his escape was he had a bag he could refill with a psychotropic substance [LSD-type] to help place a subject into a state of mind conducive to revealing more than they should [Bit problematic, I know - I've actually been rethinking that since posting]
The drawback of Death if he tries to reproduce too much material is, I thought, rather appropriate for that useful of an ability. That was the point of the Incident report - Whoever's holding the container has his/her mass used for the 'refill'. Typically, that'd be him - And he's no Wolverine/Deadpool/Deathstroke/682/Etc… He heals 'somewhat faster' than normal, not instantly - if it's more than half his blood by volume, or too dense a material [Which hasn't been the case thus far], he's not getting right back up and going for more - He's going to the hospital. He just *will* eventually heal from anything that doesn't immediately kill him. Heck, the only reason he doesn't appear to age is that he gets a regenerative 'spike' whenever he makes something, which takes out the medical ailments of aging. And that coupled with extensive usage of the ability is why he doesn't just collapse into hypovolemic shock whenever he makes something over a couple liters in volume [That, and it 'grabs' waste material, then bodyfat, then plasma, then non-vital organs… You get the idea.].
I have read the first 1700 SCP files, including 'God', 'Abel', 'The witch child', 'Cain', The little girl that imperfectly follows any orders, the Butler's bell, the little girl that makes anyone want to attack her then have a heart attack, the little girl that can transmogrify animals… He is hardly OP'd, just resourceful and a bit paranoid, as he made his living dealing with drug addicts/dealers and cops prior to capture.
Actually - now that I mention that… I'm going to be taking the Breach attempt out. The Foundation has got to be better than prison, in which case he'd likely be actively trying to seem harmless and helpful. Going to leave in the attempts at peeking into things he shouldn't, though :P
Besides, they probably search his cell whenever he's not in it, and he'd assume that and not be careless enough to leave blatant evidence laying about.
The article does clearly state that the duplicate isn't exactly the same as the original. It's 'enhanced' - ie 'changed' - not always in a good way [note the dead fish experiment] And the 'enhancement' comes from the adding of his own DNA into the mix, which is basically standard-human. Other than that and it not immediately rotting, very similar to 'The everything tree' products.