I have a backup handy, but it's not something that I'd necessarily trust for extensive use, and it's only useful if I'm actually home.

In other words, if I need to switch to it to fly out to a one-off and I'm already home, it's fine. If I'm going out on a four month long tour, I really don't want that to be my main bag for for months. And if I'm in the middle of a tour and thousands of miles from home, that backup is useless to me.