Having had several Volvo's I must admit I fell in love with DRLs a long time ago, and have fitted something like it on every car I have ever had. Actually, I love lights... as far as I am concerned, you can't have enough... If I could afford it, I would turn my T2 into one of those Japanese Dekotora trucks.
The laws on DRLs are fairly simple...
On with the Ignition/engine running...
Off, or dimmed once side lights are turned on.
Personally, mine come on only when the engine is running, and dim when I go onto low beam... The reason for me, is when acting as a rear end protector, doing road searches with KSAR, headlights can hinder the eyesight of the searchers, so we run on sidelights, but the DLR's just help give me a bit more light in front of the car, and makes me more visible to the idiots who don't slow down despite all the flashing lights, and people in florescent clothing, but does not dazzle the searchers.
It has been through 2 MOT's like that, and they have never picked up on it.
You do get what you pay for, the cheap ones rarely last the year. The more expensive ones should have a Metal back, with fins to dissipate the heat from the LED's, if it does not, then the LEDs are either not high enough power, or will cook themselves very quickly.
The ones I got are simple, on with ignition, and off with side lights, so I bought an extra box from Hong Kong/China to convert them to dimming.
If you buy the right ones, and have the facelift later T2's, they fit perfectly in the indent in the front bumper, or on the earlier ones, with the round headlights, they recess nicely under the fog light...