I also think having 2 lights is better because one can be run at the full 250 lumens to see while the 2nd can be run at the normal lower setting as a "see me" light, thus ensuring you'll rarely, if ever, deplete both batteries on the same ride at the same time.
Certainly having two lights offers more versatility than just adding the lumen output together. However there is one fundamental drawback of using a series of underpowered light sources. All else being equal, multiple
lower-power lights will never add up to the " identical throw power" of a
single more powerful light source and reflector.
So a key part of any lighting system is the maximum distance of user-acceptable surface lighting. In this case, a light system that uses two emitters side by side in a single case should not claim to double all aspects of the lighting patterns associated with a single emitter......