Just to add confusion, there are two of us Clives replying to your post!
For further confusion, I incorrectly referred to the noise absorbtion mat as Isolator 10 - it's Isolator 8 - it's 8mm thick. Here's the product which I fitted on top of the Ground Zero sound deadening mat.
Yes, Dynamat Dynaliner is a very similar product to the Silent Coat Isolator 8.
As the other Clive says, the increase in weight is negligible - both noise deadener and absorber together weigh about 3.5 kgs/sqm and I used 3.3 sqm to do the whole of the cockpit floor, door skins and boot floor - so you may be adding about 12 kgs to the car's weight.
Whether you decide to go for the absorber as well as the deadener is up to you but, again, as Clive says, the benefit of the absorber will be far less noticeable than the deadener.
Hope this helps.