Design Text Here---You can't get more flexible than a modular system. For vegetative growth install Cool White and Blue modules, and for bloom phase switch to Warm White and Red modules. Throw in a little green and yellow for good measure, and fine tune the light spectrum to exactly what you and your plants want.
Many high end commercial LED grow lights now offer the ability to switch on the Red only, the Blue only, or both at the same time; this is a very limited flexibility. Some units include built in timers with remote controls; while some may see that as flexibility, many are just paying for unwanted features. The ability to dim the lights may be considered flexibility to some as well, but we fail to see the usefulness of this feature here at Build A Sun; we strive for more light, not less.