RH,
I've heard of the practice, and I think that maybe I've even tried it once, but typically I don't bother with worrying about it....I simply give them a good home, dump them in it, and try to leave them along until they get settled.
Not sure if I'm doing something right or it's just dumb luck on my part, or what....but I've had little to no problem with swarms absconding on me. :-D
However, I did catch a couple last year where I put eyes on the queen and decided to cage her for a few days...As it turned out, I did witness one of those reswarm and have to return because they didn't have the queen. :laugh:.....That was pretty cool!
I was in New Orleans for the day yesterday and got a call from a co-worker, his neighbor had a swarm in his tree. I managed to get home and there JUST before dark so I decided to vacuum them up. I left them in my catch bucket last night (well ventilated) and need to go hive them this morning.
As usual, I had absolutely no intention of using an excluder.....but now you have me thinking about it and second guessing myself. lol! :laugh:
I would agree that if you do use one, three days is probably sufficient to assume they're anchored and won't leave on you.