So I finally got a chance to get in a few rounds with a first gen Simian to compare it against my Ergo, and I can say I made the right call with the Ergo. I played three rounds yesterday and split bag duties. I started with the Ergo and switched to the Simian. After the front nine, I couldn't wait to finish to restock the Ergo for round three. While I know the current gen Simian has seen a lot of improvements, I just don't think they would be extensive enough to change my mind.
Specifically, I can't fit nearly the same amount of discs in the main compartment to match the Ergo, which severely limited the extra stuff I could carry because I had to pack the side pockets with plastic. The frame was the main reason for the limited space. While there was room for more discs in the main compartment, the PVC fittings shrunk the width of the opening and wouldn't allow more discs without some serious force when both loading and unloading.
As for how the bags sit, I prefer that the Ergo sits higher on the back, and the frame is undetectable due to it being on the front of the bag except at the very bottom which is very thickly padded. The Simian sits most comfortably down lower like a traditional bag, and that didn't mesh well with me because the straps (even being as short as I am) weren't long enough to cover the entire contact area on my shoulders. The buckles were felt in my armpits which made me tighten and loosen the straps as I put on and took off the bag. I want to make it abundantly clear that the straps on the Simian have been redesigned and look more like the Ergo's in terms of both width and padding than any other bag. The first gen's however were the width of the Grip with even less padding. While the Simian felt great on my back when I first got it, the straps became an issue when I packed it with two full 32oz Nalgenes. That was a very frustrating surprise. I know I could use quads instead, but I could get mine adjusted to fit as comfortably as the included straps. I'm sure the current gen is much better so this part is apples and oranges unfortunately.
I also didn't like that the water bottle holders are attached to the side pockets (I always wondered how little or how much they would sag, even before the Grip bag existed) which made setting the bag down an extra hassle. The water bottles did help keep the bag upright on the side of a hill though, regardless of which way it was facing, which was awesome and a big plus over the Ergo.
Something else that might have changed with the updates is that there were no real "technology" pockets. Because I had to pack the side pockets with discs, that left only the underside storage area. There is no way I'm putting a phone that cost as much as the bag where it would be the second thing to hit the ground next to the water bottles. The side pockets would've given my the same worries too since they have no extra pockets either and sit flat against the ground as well. I really love that the Ergo's tech pockets (my description) are high enough on the bag that anything in them is safe when pulling out water bottles and discs.
Now to the thing the Simian has that the Ergo doesn't, the seat. It is certainly nice to have a seat be part of your bag so it's never forgotten at home or on the course. Even with substantial padding, my 200+ lb body was heavy enough that I couldn't feel anything but the front and back of the frame. It was not completely uncomfortable, but I was pretty disappointed. Hopefully this was upgraded with the current gen as well.
Well, that's about it. Sorry for the novel.