The GP Thunders are a simple xenon bulb replacement for the oem DRLs. Most people will use a higher temp bulb like 7500-8500k to get a purer white light with slight blue tint, versus ugly yellow oem.
I personally don't "get" the whole angel eye mystique brightness thing. I mean, for brightness I turn on the damn headlights. But for daytime running lamps all you're looking for is a little accent around the grill. Better light distribution between the inner and outer ring is the only concession I would make towards getting the higher-end lights (Aib, LUX. etc), but not for the $$$!
I JUST finished putting in my GP Thunder 7500ks. They look GREAT! Very white color, cost me literally $14 and took 10 minutes to install. Now they do dim down with the main headlights come on, and the color could be a little "whiter"--in hindsight I would go with the 8500k--but this was just the simple solution I needed.
2008 M3 Coupe / DCT
// StopTech BBK 380/355 / Pagid RS29 / Motul / Apex Arc-8 / BFG R1S / Ground Control / MS filter / Performance spoiler / BPM tune // Road Atlanta 1:39.80 / VIR Full 2:12.32 / Barber 1:42.20