I had Marathon Plus tyres before changing to the MTB version, mistakenly it seems thinking that they were more puncture proof. I've had loads of punctures with both types with the added pain of trying to remove said tyres, at one point resorting to a screwdriver to break the seal with the rim.
The Slime, as I said, has been hit and miss. I have removed five thorns at the same time and the tyre has remained inflated but it has alas gone down with one thorn in it. Any slime in the tyre I have found easy to remove with wet wipes, although a bit messy.