The 5863 is very similar to the 4133 Super Set that Andi reviewed back in April 2006 here:
http://www.playmofriends.com/forum/index.php?topic=663.0Ther only difference I can see is the figures, this set comes with only 3 figures not 4, and they're different figures, so here's a close up:
The attacker is the 30 00 1322 War Duke from the 3268 Knight's Empire Castle, the two defenders are simpler figures, but useful as they fit into many possible groupings. I'm tempted to swap their legs over to give one heavily armoured knight and one much lighter armoured archer.
A question asked of Andi was, can you build a Steck tower on top of the base? The answer is yes, but not using the lugs provided. You can however fit a 1x1 tower inside the existing battlements:
I've used open side pieces for clarity, and you can see that the trapdoor still opens. The tower fits very neatly inside the battlements, and a blob or two of blu-tac suffice to prevent slippage.
The 4133 set is still available in several shops I've looked in, so it's a matter of figure preference whether you go for that or this version, but either set makes a very nice small outpost with lots of play value.