The fret are easy to remove from the BL1 (as long as you are not short and do not have a stool or chair to stand on). There is a gap at the top of the fret where you reach in and push on a small latch/button which unlocks the fret and then it just slides up. It took me a while to find it the first time, but it is really quite simple (it is in the middle gap, a little to the right). It is true that the mid-range driver is behind a mesh dome so you cannot easily see the driver surrounds. However, I've not heard any mention of foam issues out on this forum or elsewhere (and I did a pretty thorough search prior to buying).
Since I own BL1s, as you predicted, I say they are "all aces". I don't have any experience with Pentas, but I was at a US service center a few days ago discussing repair options for my BL1 (the on/stand-by LED isn't working properly), and he had some pentas in for repair, and it was his unsolicited opinion that the BL1s "blow away" the Pentas (I just mentioned to him that I had never listened to Pentas, and he offered his opinion - "muddy" sound is a comment I recall). He wasn't trying to "sell" me anything because his advice was that since the speaker works otherwise, it could be a costly repair (as you may have to replace the entire amplifier board) for little value. I realize this goes against the conventional wisdom on this site (Pentas rule, BL1s are just OK), but also points to the fact we all hear differently. I think they are quite a bit better than the BL8000s (which I also own). I don't think they were a very good value at $8K (which might have something to do with their lack of love on this site), but if you can find them ~$3500 (and they're in good shape), I think they're a great value.
Stan