A thought occured to me while I was using the Kre-O sets to build a few mechs. Lets take a look at how parts compare between the two block systems.
In this first picture you can see a side by side comparison of similar blocks. The first difference you can see is the one between the colors. The second is the design difference between some of the pieces. Overall, if you know what you're looking for, you can see the differences but, to the "untrained" eye there is not much difference.
This picture contains parts that are not duplicates of Lego parts. Well, the upper right and lower right pieces are similar to Lego pieces but I thought they were different enough to include here. The top right corner piece is similar to the standard Lego dome piece, just a little shorter. The one on the lower right is similar to the Minifig Utensil, Handlebars.
The modified 1x1 round brick that looks like a gun muzzle has already seen a lot of use. The one beside it on the left could be useful as an "underslung grenade launcher" on a gun or maybe as some sort of "heating/cooling unit" on the roof of a microscale building. The middle piece on the right -- the brick with two clips on it -- has a lot of SNOT potential. The most interesting of these pieces in terms of sheer building utility is the double male connector in the top row.
After buying the set these parts came from I'm really tempted to buy more and see just what I can accomplish with a greater selection of them.