We've got the bamboo ones too. I bought ours as an overnight nappy as I generally use the bumgenius for daytime but they weren't lasting overnight.
I did look at the microfibre ones and there didn't really seem to be any difference between them to look at.
Yes, they are different brands buy microfibre is not supposed to be quite as absorbant as bamboo (yet my BG's will still last 3-4 hours depending on the time of day) and they do dry a lot quicker than the bamboo. I tend to find that even with my tumble dryer I still have to hang the bamboo bits out for an extra hour or so compared to the microfibre ones (think this is due to our TD as it stops drying once not getting sufficient water out, so the amount from 3 bamboo nappies wouldn't be enough to warrant the cycle continuing).
Realistically I think it's personal preference. Microfibre are good for day use but if you happen to have a heavy wetter then it's good to have a few bamboo ones for night time.
My only slight complaint with the pop in is that DH finds them very difficult to get on for overnight use with all the inserts. Even I find it a struggle at times as there are so many layers and there aren't sufficient snaps to snap all the layers together. This adds to the fun of getting it on a wriggly older baby as they tend to move and pull the night booster away from the rest of the nappy so you have to get insert and baby 're-alligned' to get it on.
Another store to check out is www.thecottonnappycompany.co.uk who often have good deals on the pop ins, and other brands.