One thing to be aware of is that most hobby compressors state the displacement. due to losses this is a higher figure that what you will get out of the compressor which is known as Free Air Delivery or FAD.
Typicaly the FAD will be 50-70% of the displacement. Hence my post yesterday where I said 8CFM( 225l/m) from mine when they are sold as 11cfm as that is the displacement but just looking it is acually less than 8cfm.
So if the screwfix ones are single motor expect 60-75l/m out of them.
Yes the 8 and 24 are the tank capacities, I have a 50lts