One key difference, that you can see in the photo, is that the BV uses buckles instead of Velcro on the straps that attach the bag to the underside of the saddle, something much more important than it may seem. A pair of bike shorts (or any shorts) will shred quickly if they’re rubbing against that tiny bit of Velcro protruding from the side of the bag, and it’s sure to destroy expensive sweaters and gym clothes if you stuff the bag into your backpack or messenger bag.
A wrench that fits the hub nuts: If your bike has quick release front and rear wheels, you don’t need this, but if you have an internal hub on the back, such as the NuVinci, a wrench that fits is a great idea. 99% of the time, this is a 15mm wrench, but you should check your bike. A 6 inch adjustable wrench can also work, but it will be heavier, and when using an adjustable wrench, you do need to take more care to not round over the nuts. A fixed wrench is the best choice. Some multi-tools have a 15 mm wrench built in, but again, if you have limited hand strength, something with more leverage is a great idea.
As you mentioned, it is surprising how often you can get multiple flat tires on while riding, particularly on longer sprints. The tip about bringing a patch kit in your bike repair kit can be incredibly helpful if you’ve already had one flat tire. I agree that all you listed seems like an awful lot to carry, but it’s always better to be safe than sorry, isn’t it?
First, I researched. I looked at Amazon’s top-rated products and their user reviews. Then I consulted Bicycling magazine, Gear Junkie, Bike Radar, Outside, and the occasional bit by Lennard Zinn via Velonews. I also found some worthwhile discussions at Bike Forums. Then I spoke with four experts, Ramona Marks, Scott Karoly, Cari Z, and Alison Tetrick, riders from all across the spectrum, who tour, repair, and race.
The fabric attachment system is low-tech, but that seems to be helpful, as it can adapt to seat rails of different widths. One fancier option you might see on more expensive seat bags is a quick-release mount that you install under your saddle. But those have a fixed width, and therefore can fit under seats with only those exact specs. Brooks saddles, for example, are too wide for these mounts.
Pedals are important because the serve as the contact point between the rider and the bike’s transmission. Clip-less pedals systems come in a variety of designs favoured by individual manufacturers, but the mechanics of all styles are roughly the same. Tiny adjustments in the position of the show cleat – that snaps into position on the pedal – can make a big difference to the comfort and health of the rider.