Right mate. First things first, you will only ever get minimal performance gains from an induction kit.
Lots of manufacturers and shops claim big power gains "10bhp from fitting a viper to a 1.1 saxo!" Truth is, it doesnt and really only improves the responsiveness of the engine slightly. (How freely it revs and the time it takes to do something after putting your boot down.)
You may hear a few people mention "heat soak" this "phenomenon" is where the air in the engine bay is heated by the engine and therefore renders open filters pointless! (As they are gettin warmer air instead of cooler, more dense air.) This is not true so long as the car is moving, as soon as it is moving cool air pushes the warm air out of the engine bay. Hence why you see open filters on say, Skylines!
If you want a filter that makes a shit load of noise and improves the performance pretty much as much as the next filter i would recommend an open pipercross!
However, if you want to take the tunung of your car a lot further, an enclosed may give you that extra 0.2 of a bhpto get over a big boundary say 150bhp.
End of the day mate they all pretty much gonna do the same job in a 1.1 - 1.6!