If you depart from fully instrumented airfield, you will still need to fly that amount of time to get yourself into some position to fly back, enter a hold and do an approach!
Huh ? If you tell the tower that your intention is to fly approaches then you depart the runway and basically begin with a MA leg before talking up a hold or a procedure.
Believe me, that doesn't take as much time as flying from Stapleford to Southend. Whether you like it or not, EGMC is 20NM from EGSG, or about 12.5 minutes @ 110 KTS direct. A missed approach leg at most airports is not even half that length. And you have to fly back to EGSG when done.
As I said before, this can be accommodated with clever planning from the instructor, but you cannot make the distance go away by sheer willpower or marketing.
The more a think about it, the more I would suggest that the OP make a pro/con list, especially when comparing EGSG with EGMC (and EGMH). Landing fees and ground travel time to get there and comparing those with the proposed training schedule would be two things at the top of my list. That requires talking to instructors at the various FTO's/RF's.
A lot of people I know who built hours in the US went on and on about it being controlled and how they'll be prepared for airline world.
A lot of people I know trained / built hours at non-towered fields in the US. Usually aircraft are slightly cheaper to rent from those places.
you have to be very vigilant with a good situational awareness
You spend most of your time under a hood or with foggles, leaving the (non-navigational) situational awareness and the vigilance for other traffic to your trusted friend in the RHS with tig hours.
A priori, you could say there is a safety argument for doing your training in controlled airspace, as the RHS then generally doesn't constantly have to divide attention between looking outside and instructing you. But I dare say most instructors can cope with that.