It's relatively illiquid in that:
a) You have to find someone willing to spend say $20,000 on 1 coin;
b) A bullion house/dealer would only give you bullion price, about $11,000 for its metal value;
c) If you needed for some reason down the track say $5,000 for something, you have to sell your 10kg coin for about $20,000 (hopefully) and then have $15,000 cash you dont need. If you buy 15x1kg coins instead of the 10kg, you could sell just 5 of the 1kgs off to make the $5,000 in cash you need and keep the remaining 10x1kg coins. Point is, the 10kg is not divisible !