So I received my S25 in the first batch of those that went out, and have been using it for a couple weeks now. I thought i'd post up my initial thoughts.
This is my first bag with Tom Bihn and over all i'me very happy. The quality of the bag seems above exceptional. It just feels well made, and not cheap. It feels like what it costs, if that makes any sense.
The bag holds everything I needed with ease, though I do think i'm going to need to get some extra accessories to help with my organization a bit. Pro Tip: The included keychain strap is too short. Pony up for the longer ones!
One of my concerns was accessibility of some items without having to take the bag off, and i'm happy to say that this has worked out well. It DOES take some practice, but it is quite doable to loosen the straps, slip out one arm, and sling the bag forward to access the two side pockets. The trick is to get in the habit of loosening the straps or else you will be struggling. The cool thing here though is loosening the straps is very easy and quick. Just grab the buckle with one hand and lift and gravity does the rest.
The first few days I found the zippers hard to use, especially one handed. They are getting better, but still tricky in some situations. I'm not sure why this is, but it seems to be more about how the zipper travels along the path. The bottom pocket is the worst offender in this. It has this sort of hump in the middle and is almost impossible to operate with one hand. To be clear they all travel fine if you have a free hand to hold the bag. Its just when you have your hands full and try to open them with just a pull on the zipper that the problem occurs.
My biggest concern right now is the cache with rails. The first week or so getting my 15" rMBP in was really quite tough. I think now it has started to stretch a bit so it isn't so hard anymore, however getting it back out is still real hard. You essentially need to get one hand on each side and sort of roll the fabric back with your fingers while pulling up on the macbook with your thumbs. Its tough and ackward, and hopefully this will get easier over time.
My biggest beef though is I am not all that comfortable with how well this cache will protect my macbook. I never owned the previous BrainCells, but from the pictures they look like they give a lot more protection than this cache does. The cache is essentially a thick material sleeve, and thus it seems better for protecting against scratches rather than any impact. Also since the bottom of the cache is no thicker than anywhere else, i'm constantly afraid i'm going to put the backpack down too hard and damage the side of my macbook :(
I will say however that the cache sits in there nice and secure. In fact I have gone on jogs with my macbook secured in the bag and had no problems with the cache breaking free, despite being bounced up and down over and over.
Overall i'd give this bag like an 80% rating based on my requirements and desires. I'm very happy with it, and quirks aside my only concern is how well its going to protect my macbook over time.