Vehicles with headlamp-based DRLs come equipped with Long Life bulbs. These are exceptionally warranty-friendly and conducive to use as   DRLs due to their long life, but their output is low and the beam focus (and resultant beam reach) they produce is poor, due to the filament modifications made to get extra long life out of them. This is a bad trade: A very small potential increase in daytime safety for a very large and definite decrease in nighttime safety. (NB this particular disadvantage doesn't apply to HIDs run as DRLs...but those have other disadvantages.) Headlamp-based DRLs are convenient for the manufacturer to implement, and are legal in almost every country that requires or permits DRLs, but are really the wrong way to do it.

Regardless of bulb variant, using the (filament) low beams as daytime running lamps   shortens the effective life of the bulb in terms of days' runtime between bulb changes. Not only that, but headlamp-based DRLs are not optimal as DRLs in terms of safety performance, and they consume significant fuel. Using headlamps as DRLs is akin to opening the fridge door, pulling up a chair and using the fridge light to read a book! There are much better-performing and less costly ways of implementing DRLs.

For retrofit purposes, the best implementation is the full-time operation of the front directional signals (except, of course, when they are operating as signals or the parking or headlamps are switched on). Directional signals produce a light distribution with a wide conspicuity angle, are generally well located for DRL service at the outboard edges of the front of the vehicle, consume considerably less power than any headlamp-based DRL implementation, use less-costly light sources of generally much longer life than any headlamp bulb, do not encourage improper nighttime use of lights, and do not require additional lighting devices to be added. Most recent Cadillacs, Chevrolet/GMC large vans and minivans, some Toyota and Lexus models, certain new Lincolns and
assorted other vehicles use this implementation, which is legal in the US and Canada.
       
You can easily enable this functionality in your vehicle using a DRL-1 module ($42 from me, see installation instructions here ).

In the case of the ML, the parking lamps are also the front signals, and if the lights are turned on in the daytime, the instrument cluster and MCS screen also stay brightly backlit.

Is it still worth it?