The Scottish Resistance carries 50% more stickies in reserve, can lay down almost double the amount of bombs at once, and can selectively set off which bombs you want by facing them, instead of blowing them all at once. As an added bonus it can destroy enemy sticky bombs, where all other explosives simply knock them around.
On the downside it has a longer priming rate (0.4 secs) which effectively keeps the demoman from airbursting in direct combat, one of the main forms of attack most demomen use. In addition since you can only detonate the bombs you can see you cannot use it for indirect damage.
The Scottish Resistance is awarded for achieving Milestone 3 (Complete 17 of the Demoman achievements)