Thorpe are using their terrible operations to upsell terrible products like this, if their operations were anywhere near where they should be there would be no need for it... just one fast moving queue. If you don't visit very often you won't get value for money, and if you do visit often, why do you need fast pass for rides you will have already ridden numerous times?
I have never seen ride staff look so disinterested, slow and generally careless at Thorpe than on my most recent visit; I don't think there was one instance where a train was dispatched before the other one was back, parked and waiting for at least a minute. Colossus's operations were outrageously bad, with dispatches taking around 7 minutes every single time... how can they have been allowed to slack that much?! They are neglecting their ride lineup, operations, park appearance; all in favour of IP's and quick cash-grabs such as the above.
My advice? Use the money to go and ride Icon, which will most likely be running two/three trains with staff working quickly and professionally with a queue usually less than half an hour. You'll probably have a lot of money left over as well.