DTA and Emerald can do electronic boost control - don't know about the Weber stuff. If my experience of the Emerald is anything to go by, it's not advanced enough to give any significant benefits over just actuator control. Granted you can run lower boost at the flick of a switch, but the rest of the time the boost is not consistent enough for my liking - and that was after 20 hours or so of calibrating the PID control!
What do you want from the EFI system? I wouldn't worry about having boost control myself.
The advantage of using a G40 ECU is that all the cold start mapping etc. is already done by VW - who have put thousands of man hours into the calibration. It works well with the 6psi boost switch modification, and can be mapped to a refined level in a day. I've yet to get my Emerald K3 ECU running my car as effectively as I did on G40 Digifant - despite putting something like 100 hours of effort into the calibration AFTER a visit to Dave Walker.
The aftermarket ECUs in the sub-£1k price bracket are good value for money - but have had nothing like the same amount of hardware, software or calibration development that original equipment ECUs have, and sometimes that shows. On the other hand, they're easily DIY configurable and calibratable - the same can't be said of OEM engine management systems!
Other systems to look at are MBE, Omex, and Nira. The likes of Bosch Motorsport and Pectel (Cosworth) and similar companies also do systems - but you need motorsport budgets too!