Just an update.
Review of upgrades after a few weeks use.
Riding postion over standard brompton feels loads better. This is how a qood folder should feel in this respect. Its also adjustable , which is a bounus. Wish brompton offered something like this as standard, or mezzo for that matter. It takes longer to fold, but I have taken it shopping a few times and its ok. Forgot how fast mezzo fold is by compairasion. I transported 10 litres of paint offer day in front bag off road and it coped reallly well. In the rear bag of mezzo would have been unwise. Its much slower than my mezzo, yes its got rear suspension and standard tyres, but i have ran them on black mezzo before also.
Real let down is the lack of brifters and more speeds, the set up I have with gear next to left lever is fiddly but managable. Brompton is also better out of the saddle than mezzo due to mezzo stem arrangment means you need to keep arms very stiff.
Had problem with stem slipping on extention bar at first, but changing to anodised one from a satori hallo sloved this. It is very stiff to close and I have removed the saftey clip from the dahon stem as it makes it hard to fastern. This is a problem if you want to lock the bars in the folded postion. Problem is pressure on rack as forcing it closed.
Still need to tidy up cable routing , but it works the way I have it set up now
Overall big improvement over standard brommie ride and fit,it folds as compactly as a standard brommie, but is an upgrade deadend without spending a lot more money on frame wheels and levers to get brifters to work to compete job.

Dahon stem removed from birdie as adds to steering issues on this make. Bullbars would make a birdie handle very badly I feel.