i have the cold air intake. it is different from the one pictured on their website. here is a couple of pics


my car already had an aftermarket exhuast system fitted when i got it, so i didn't need the mx5 factory one.
it's been on the car for a while now, i had it fitted not long after i bought it. so my memory of the car before i had it fitted is a little vague. but i tend to recall that it really openned up the revs thru the mid range, it doesn't feel choked like it use to , the engine could breath a lot easier. oh, and it sounds a lot better now too
i think it's definately worth doing. i think there are cheaper options out there when it comes to cold air intakes, but i don't have any experience with those. all i know is that i like this one.