I just switched to them a while ago, i am happy that i did it. I'm in vegging stage as well.
For flowering everyone suggesting HPS. If you have a chance (grow room setup, budget etc) to do it, don't even think about any other options. But if you don't have a chance like me than these bulbs are looking like the best alternative, based on their lumen output I'm sayin. T5 HO's are also.
Previously i went to flower with 2500k CFL's (250w in total). Seemed ok to me. Here you can see 6x23w + 1x26w + 1x18w i used on two plants. 182w in total and 12450lm for 50x100 cm. 5.38 square foot, 2300lm per sq foot.
I can't compare the results with HPS coz i never used and i am not able to use. I don't have good air circulation and exhaust system and it is not possible for me. And my grow area is not square. Its 50x120 rectangle. These are giving me only some limited options for best economic use. But i believe if i would use over 3500lm per sq foot i could raise the yield much more. I was planning for 55 or 80w PLL but they are longer than 50cm, which they will not fit in width. And again they will not fit lengthwise equally either. In the end i set 4x36w in width and equally. There is still enough space for additional bulbs. For flowering i am still thinking about options. More PLL or use my old CFL's.