OK, yes I have done the "run off until it gets cloudy" thing for years, with a kettle screen just to catch the leaf hops. It works, and if you're anal like me you can funnel-filter the leftover wort and use it for OG, FFT, speise, starters, or even add back to your ferment if you feel brave, or save it for a mixed garbage surprise beer when you have enough built up in the freezer. I do all those things.
I've never been totally happy with it though, because I often brew smaller batches and don't like the "waste", and I do more lagers than ales and have long suspected that keeping junk out of the fermenter was more than just a good idea. My recent comparisons proved to me that at least on my system, the malt and hop aromas and flavors can get muddled otherwise.
But what broke me was getting into IPAs recently. So how do you deal with a pound of leaf and pellet hops? Dumping that into the primary is not going to happen for me for a lot of reasons (yeah, I'm a whimp compared to that dude upstream ;-)
It created a stew that defeated my regular processes, so I had to change; hence the spider and bags. And once I did that, I was surprised to see how much of the trub in the bottom of the kettle was due to hop residue, not break material. That means to me, cool, that is that much more wort that I can get into the fermenter if I refine this process. I don't care to throw paint strainer bags into the boil, that's for sure.
Hop blocker looks great, but I've seen enough so-so reviews that I hesitate. And whirlpooling... well it took me a long time to ride a bike as a kid so maybe rotation just throws me for a loop.
Paul's right - you gotta lose beer or wort somewhere in most systems, and I like the kettle myself due to the built-in sanitization. So I like my current deal better than any other systems I've tried. For me, it means more harvested wort and less work, not less and more, respectively.
To the OP, I do think that fly swatter would clog, so I'd have a backup plan in place. Also, can you move it to the side, in case you are normal and can whirlpool. It would last longer, if so. Also it would be out of the way of your IC if you use one.