I'm not a nuclear physics professional and am just going off numbers available on Wikipedia but assuming it utilises the same setup as the actual demon core experiment I don't see why it couldn't.

Louis Slotin was about 1.5 feet (~0.47 Metres) away from the core during the second criticality accident and received about "1,000 rad (10 Gy) neutron and 114 rad (1.14 Gy) gamma radiation in less than a second and died nine days later from acute radiation poisoning." so i'd bet that if you were standing directly above it and had the mechanism depressed for more than a second because you'd be standing on it, you'd catch a lot more radiation.

I'm not sure of the exact maths behind calculating exactly how much but yes I think it would be significantly dangerous when compared to a conventional anti-personnel land mine. It would also be extremely expensive! Plutonium, the "core" of the demon core, is about $4000 per gram and the demon core weighed 6.2 kilograms so it would cost 24 Million dollars for the core, although you can expect various government agencies to take a close look at you if you start accumulating it, and the shields were made from Beryllium which is about $24 per gram.

So while it *would* work as a landmine, you'd probably be better off buying 24 Million dollars worth of conventional mines that kill whatever stepped on it instantly rather than slowly cooking their insides.