The plates with holes are restrictor plates. The aim of these is to restrict the flow of exhaust gas without blocking it completely - a full blocked EGR valve will cause a 'Check Engine' warning light to appear on the dash, and this will be a MoT fail in the UK. A restrictor plate should allow you to continue to run the car without any further modifications. I ran my car with a diamond restrictor plate for a couple of years but I can't say I noticed much, if any, difference. If you're going to use a restrictor plate it should be stainless steel rather than aluminium, the latter could be weakened by the heat of the exhaust gases and bits of it ingested into the engine. There is an 'official' restrictor plate which is square with 4 holes: this fits between the EGR valve and the inlet manifold. The diamond plate fits between the EGR pipe and the EGR valve (on the 2.4 engines, 1.9 or 2.0 may vary)
The plates with no holes are full blanking plates and you will find the car runs a lot better with one of these fitted, albeit with the 'check engine' warning light. You can buy a dongle (Fixitsan) that plugs into the OBD socket to auto-cancel the warning, or the ECU can be re-mapped to 'forget' that the EGR ever existed.
Last edited by dastocks; 13-07-15 at 15:30.