There are three issues with the use of speedbrake on the approach
1) They cause significant buffet on the tailplane (extreme at Flap 30) for which it is not 'lifed' in structural testing or design. Most airlines in my experience (737) prefer not to use them above Flap5. If you doubt me, wait until you are seated with a view of the tailplane when someone uses flaps and airbrake.
2) They increase the stall speed and make Vref no longer valid as a guide to 'safe' margins
3) Most airlines forbid their use below 1000'.