I am presently using the ISM saddle and the Bisaddle. So, sit back for a bit of a long story. When I first started tri, saddles were a nightmare for all the reasons most people have. I eventually settled on a Fizik arione tri because the nose was narrow enough I could rest my weight on the pelvic bone to the left of my repro organs. Not perfect, but I could do an hour that way and I don't usually go longer. I could swap to the other bone on the other side but was never as comfortable. I always thought I needed a saddle with two noses.
I was out of tri for a while and when I came back, I had an ISM in a box from a complete bike I had bought used. I tried it and found it terrible. One day I was looking at it and thought, what if I forced the two nose prongs apart to create the two-nose saddle I want? After a couple of failures, I tried using a bolt with nuts to push against each other and that finally spread the prongs apart enough that I can sit on both side pelvic bones. Now that is my tri saddle.
At the same time this was going on, I bought a bisaddle to try and achieve the same effect. When I first was fiddling with it, I was pretty disappointed; the bisaddle nose is flexible and soft. Then I realized it was not meant to be ridden like the ISM at all. Further fiddling over the course of a month or six weeks yielded the most comfortable, all-around saddle I have ever used. However, I started with the SRT and though I loved it in the aero position, sitting up climbing was uncomfortable because it lacked sufficient padding. I was ready to send it back but called bisaddle and they said to try the Bonneville which is the most padded saddle they sell. They immediately sent me the saddle parts needed and just said send back the ones you decide not to use. The Bonneville's extra padding made all the difference and now it sits on a seat post that I use for my gravel and my all-road bike that both have aerobars and a dual-position seatpost. It is easily the most comfortable saddle I have ever used and also showed me that I like a nice wide saddle. The bisaddle is about 155mm wide where I have it adjusted so I tried another 155 saddle for a road bike and found that pretty comfortable (I had always used 143mm saddles before).
On the SRT I still rest my weight on my pelvis bone with my reproductive organs off the front, but with the Bisaddle you sit on the back of the saddle with everything in the very large cutout in between. (I just measured the gap and it is a full 5cm gap on the bisaddle).
Sorry, that was long, but perhaps it answered some questions for you.
Just to reiterate, I had to alter the ISM to make it work for one style of sitting. I use the bisaddle on two bikes that do a lot of climbing but also both have aerobars for riding alone into the wind and I can ride those aero positions "all day" because the bisaddle is so comfortable.
The great thing about bisaddle is that you have 90 days to make it work, and they are super helpful if you have questions. I went through several iterations of adjusting it. I tried the flat version with the wedges and didn't like it. I tried the nose really far apart and did not like it. When I finally figured out how to ride it and received the more padded Bonneville, it was that moment after 40 years of cycling where I said, "This saddle is comfortable."

Pictures. I don't know how the level of padding is on my ISM. It is not much, but as long as I ride it at least once a week, I don't have any issue racing for an hour.
The bisaddle is great for any time and distance and works equally well in the aero position as it does sitting up climbing. When I get around to buying another (and another) I'm sure I'll have bisaddles on all my bikes.

Thank you. Much appreciated. Out of curiousity are you saying that the BiSaddle SRT you ride 'in front' but the BiSaddle Bonneville Distance (SRT 2.0) you ride 'on top'?

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Running is the best source of fiber that I know of...

No, sorry if that was not clear. The SRT and Bonneville ride exactly the same way, but I could not ride the SRT because it was not padded enough. The Bonneville solved that problem. Your sit bones rest on the wide part of the saddle and then you can just rotate forward and the weight is shared between your sit bones and your pelvic bones with the very large cutout relieving pressure in the middle. It is the only saddle cutout I found large enough to do that effectively.

The ISM saddle, in the tri position, holds my weight on the pelvic bones. Also, I did not mention this before, but the ISM is not meant to be sat on using your normal sit bones when you are back on it for climbing. It takes a bit of getting used to and I have no idea if I could do it for 1-2 hour climbs, but for ten minutes it is fine.
I'm not even sure I'm using the ISM the way it is intended with the two nose prongs so far apart, but it works for me. If you are supposed to sit further back then I don't find the cutout large enough.