I carry both the Quick Seine and the Catch a Hatch. Plus I also made a kick net with dowels and screening that a pretty good size: about 2.5 by 2.5' with longer handles.

The homemade kick net is useful for water I'm not familiar with. You have a friend kick up the rocks up stream and see what floats down to the net. I consider it a serious entomological tool, not an off-hand type of test, and good for seeing what's in the water from top to bottom. I keep it in the car; it's not something I carry around all day hanging from my vest.

I use the Quick Seine more regularly for checking the drift. It's simple to roll the netting over my net and dunk into the stream. Good for a quick check of the drift, including emergers, but it won't tell you what's clinging to the rocks on the bottom and it's too clumsy to catch anything in the air.

The Catch a Hatch works best for me for snagging airborne insects (you have to be quick) and fits nicely in an inside vest pocket. Doesn't add more weight than a stream thermometer.

All three have proved useful from time to time. You'll also want to get a key for identifying the bugs you find. Caucci's INSTANT MAYFLY IDENTIFICATION GUIDE is handy.