sells a 6 ohm 'load equalizer' to address the burned out bulb indicator problem. However, given that the LED bulbs usually are accompanied with a "Not DOT Approved/Show car-off road use recommended" label, I would not want to bet they were as effective as traditional bulbs. Likewise, I would suspect that your liability might increase (depending on where you live) for having non-standard brake light bulbs in your car during an accident.
I have toyed with the idea of adding these to the unused rear fog lamp sockets on my 87 300E as supplemental brake lights, on the theory that the instant on effect would give a 'sequential on' effect to the brake lights - the eye is attracted to motion at night, and this sequential instant-on/normal-on motion effect might have some small safety advantage. This theory comes from the original intent, design, and tests of the 3rd center brake light which was for for an extra center brake light that flashed: The rate of flash increased with the rate of deceleration during braking. Tests showed this had a dramatic effect on decreasing rear end collisions. The feds, however, said cars couldn't have a flashing red light to the rear, as people would think theyu were police cars.
They nonetheless mandated the use of a non-flashing center light, even though the control group in the tests, as I recall, showed that non-flashing center brake lights had no effect on the frequency of rear end collisions.
I may try the rear LED bulbs in the fog lamp socket idea at some point, but spending $80-100 and messing with the bulb out circuit are not real high on my honey-do lists. The rear end collision liability is not a major issue for me, as CA generally rules that if you rear end someone, it is your fault. Other states/countries may see things differently, so proceed with care.