there reliable, if u biuld them properly and if ur not trying to get rediculose power. one of my cars (242bhp at the wheels) is a bloody nightmare, breaks al the time,
the other which is standard bar a zorst, filter and chip hasnt missed a beat in 20,000 miles.
on the near standard one i get about 250 miles to a full tank (45odd litres)
so not bad. an rs turbo will be much more fun than a zetec (personall opinion)

but it would be a easyer conversion if u used a fiesta rs turbo engine because it is already using efi (ur car should already have an efi loom ) where as the escort rs turbo engine is mfi (shite management)

as long as u look after the lump and have it set up properly, it will look after u


hope this helps mate