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One has to be innovative! No reason to "bad mouth" Malaise traps simply because they are usually used to collect and kill insects. Simply change the collecting head from a killing jar to a larger cage, or block off the entrance to the killing/collecting jar. Most insects are 'quite happy' to stay alive in the trap (not actually happy but they do eventually come to rest at the top of the trap).
Vandalism can be a big problem but when I collect tabanids with my Tent Traps (essentially 'flight interceptor traps', as is a Malaise Trap) I use them for a couple of hours in the area. I then collect in the area with a standard insect net. Invariably the Tent Trap collects at least 10x as many tabanids as I get with a hand net; it also collects many more other insects that I catch with a net. In fact it usually catches so many insects that I don't have time to collect outside the trap, kept too busy selecting tabanids from the trap.
So, use a Flight Interceptor trap to trap flies, remove those you want and at the end of the day release all the insects.
Some discussion on traps:
HERE
Some of these new tent traps are 'pop-up' tents and can be set-up in less than 1 minute.