I have a Bob trailer. I used it on tour once. It worked fine, though it did add more weight and drag than racks and panniers, plus I had to carry an extra tube, and I had to change my pump head from Presta to Schrader every time I pumped my tires (I usually pump up at least every three days on tour.) I started calling it "the anchor" in my mind as I pulled it up the North Cascades Highway.

However, since that tour I've bought a new tourer with new racks and panniers, and hitched my Bob to my old, rigid mountain bike, and I use the rig as my "shopping bike". I can get 4 bags full of groceries on it.

If your touring rig is going to lead to a shopping/commuting rig, a trailer is a good option. You can tour with one just fine, and have it for shopping/commuting afterwards. You won't have to spend money on two different setups.

I like the Bob because of the single wheel that tracks behind the bike's wheels. You don't have to worry about avoiding obstacles wiith the two extra wheels sticking out. Is that a legitimate hassle? I don't really know, because I've never had a two-wheel trailer, so take that concern with a grain of salt. On the other hand, a two-wheel trailer takes all of the trailer weight on its own wheels, lessening the chance that the weight of the trailer will contribute to breaking spoke on the bike's rear wheel. The Bob takes a lot of the weight of the load, but still adds some to the bike's rear wheel. There's also the issue of low-speed handling with the Bob, and the torque it can put on the frame's rear triangle. I didn't find it to be a big deal, but occasionally it's a hassle when the trailer starts to twist things.

My 2 cents (from a fellow teacher.)