Its not legal if its sitting in your guard.. It just means the copper who pulls you over can't see the pod filter and give it a shake and go 'hey, its unsecured.. Canary bitch!'
Under the new NCOPS iirc, any aftermarket Pod filter needs to be secured in TWO locations, although the majority of the time the Pits will let you go on one if it is a good and sturdy secure fix (Like the Injen Intake). If you act like a wanker though, theyre going to clip you for both.
Its true, the jacks don't know jack shit about what theyre looking at under the hood, but they
have been trained to look for shiny bling bits, they know what Pod Filters look like and a couple of other things (I LOL'ed at the copper trying to grab the Wastegate story)
I too have also had a copper before walk around to the front of my car and ask me to pop the bonnet before also....Only problem is I was driving my MR2..