i had compbrake & they are shit .
O B P do a good selection but be careful on the pedal ratio you should be looking for around 6 to 1 ratio any less & you better have legs like Arnold schwarzennegger
as for cylinder ratio 0.700 for front & 0.725 for rear .
do not buy the cheap crap on ebay or compbrake they leak go for minimum genuine girling
preferably A P or tilton hth