A lot of the older suby guys swear that the engines need regular thrashing to clean the top (should that be sides) of the engine out and keep the lifter noises at bay...
I think the main difference between SUEC and Carby Clean is that the Subaru stuff foams and hence doesnt just drain out the exhaust valve due to the effects of gravity.
All speculation tho as like I said... I haven't used it on MY cars...
I have seen this used on Subarus... Its a foamy type substance. Can be purchased from Subaru. Cleans out the carbon and varnish deposits in the upper engine. Makes a difference. Haven't tried it on any of my cars. Suspect the subarus need it because of the boxer engine configuration...