The Atag looks a beast, great on paper, excellent, but is it proven over time? the manufacturers guarantee is good but do you take the chance because it cannot be cheap, Its not always best to pander to customers expectations and fit untried products.
If your the expert explain and teach the customer, lower his expectations if required and change their mind, offer other methods with time tried materials and reliability.
If you try to play catchup to stupid not needed performance and end up experimenting with unknown items remember when it goes wrong it's your fault, your the idiot and you have to struggle to put it right, go tried tested tell them unvented or big Worcester or walk away.
Not nice loosing customers but if they will not take a professionals advice walk away, callbacks and being bad mouthed by customers for under performing systems they forced you into fitting cost money and time
