Arundel's Dual seat bag is okay in my book. I opted for all black.
I picked this bag for it's simplicity and understated looks. I like that it uses no special attachment devices to get it on the bike... just a single velcro strap. The leather patch placement makes sense, too. Only time will tell how long this bag will last... but, I'm confident it will serve me for many years to come.
I stuffed the Dual with a spare tube, a Lezyne lever kit (includes 2 levers and patches), and a Crank Brothers Multi 17 tool. It fit's all of this with a little bit of room left. More room can probably be had if I packed a smaller multi tool, loose tire levers and loose patches.
The claim is that The Dual can fit two spare tubes... and this may be true if they are sized for a road bike. I found that it will only fit one cyclocross sized tube. This works for me as I don't feel that I need to carry more than one spare.
If you're looking for a decent seat bag... look no further.