I'm sure Steveti will add to my post , I've had two turbo conversions from BBR and my current mk 3.75 was converted 5 years ago and has performed flawlessly since then, It puts out a mere 300bhp. They also (like Steveti's) have done extensive road friendly modifications to the suspension system i.e coilovers with enough travel to cope with a road and not a race track and stiffened roll bars tuned to the coilovers and the change in the centre of gravity from lowering.
All their conversions contain a large number of components of their own design, which are then extensively researched and tested. Neil the owner has probably remapped more MZR 2.0L then the rest of the country put together, he knows that engine and it's management in great detail. Each remap is tailored to the individual engine via the rolling road, it's is unique not a generic basic map.
I have not had a BBR 200 but ran a 180bhp install from another 'MX5 expert' which in hindsight I should have paid the extra pennies. The camshaft and exhaust manifold are their own designs and you'll certainly smile at the uplift in torque and BHP it gives over stock. Sadly naturally aspirated tuning doesn't come cheap when you look at gains vs cost, forced induction gives more value in terms of output per £.
In my opinion they are very reputable company, I visit once a year for service , MOT and a chat .