I know I don't drive a Leon but I noticed this post and thought I'd reply. I was at a vag meet the other week and apparently you can run an atmospheric dv on a 1.8T, just not on the vag ecu. The guy was running a DTA ecu on an audi tt 225 engine in a mk 2 golf. Whether having a whooshy sound is worth £600-800 for an ecu is a matter of opinion. Personally I don't think it's worth it but hey, just my 2 cents.
I assume that price would exclude man hours to set up the ECU?
You can run without a MAF and a fully Atmos' DV if you are using an alternative ECU but why would you bother unless your running a seriously hybrid motor.......even then if people know what they doing you can stil retain the OEM ECU.
Aftermarket ECU's are only as good as the programmer setting it up and you will loose some of the safety features of the OEM unit.....
If you were transplanting a BT 1.8T into a Mk1 Golf or something I'd think fair enough......otherwise your just throwing away a perfectly good ECU