Firstly, this belongs in the addons discussion section, but no doubt a friendly moderator will move it
In answer to your q, FFUR is a unit replacement pack. It replaces all the units, islands etc with more accurate and graphically enhance versions. There are 5 packs I think, woodland is traditional flashpoint and you can replay the campigns in it.
ECP is different, ECP is based on enhanced effects, gameplay and AI
Is ECP better, that is a matter of opinion. Many find that FFUR is to laggy for them, and they would rather have the better gameplay than the pritty graphics (my opinion)
But some like the realistic look of FFUR, but you need a good PC to run it.
A matter of opinion really
As for the installation of ECP, run the installer and it sould just work. It sould be added to start menu, if this has not worked then
1. Right click your desktop
2. Go to new on the menu
3. Then click on shortcut
4. Then copy and paste this into the box you get
"C:\Program Files\Codemasters\Operation Flashpoint\FLASHPOINTRESISTANCE.EXE" -nomap -mod=@ECP
Then it sould run. (I am assuming you have the flashpoint reistance or game of the year edition)
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edit:
trapper beat me to it, lol