The shoot-through ones put less light on your subject, as they'll reflect about half the light backwards. This gave me a ton of problems indoors, but isn't as big of an issue outside... the lack of power is. Directional light from a big light source works for me... especially in a team of two. With the shoot-through ones being very close to my subject to compensate for the light loss, the falloff was evident across my subjects, and I had to back them up to get more even lighting. Nice shoot through ones might have solved this. I just got the reflective ones instead and adapted to the slightly harsher light.

600 lumens may be enough... (definitely enough for night MTB'ing... I started out with a 200lm Niterider Halogen system... it's amazing how far the technology has come on these in the last decade)

There are '1200' lumen rechargable systems on ebay for about $25 a pop... they're actual light output is around 800, but they're still powerful. They use a 10w Cree bulb. I haven't tried them with my umbrellas, but I'll do that this evening. Run time is pretty short, though.