This was a question that I still have not answered to perfection - not specifically the hop blocker question, but keeping hops out in general. It's like an equation with a lot of variables, like details of your system, how you chill, type of hops, whether you whirlpool and/or settle.
In general I find screens of any type work great with leaf hops but not so great with pellet hops. Hops spiders for me always clog with gunk, not necessarily hops, but kettle trub and proteins or whatever. Hop bags result in reduced utilization. The best hops flavor are from letting the hops go free in the kettle IMO. So after pursuing all these different directions, I just kind of wondered, why am I fighting this so hard? What is the big deal about a little hops getting into your fermenter from a beer quality point of view?
I decided I wanted to pursue ease of use. So I dropped anything that was fussy. I only use a screen if I'm using leaf hops, otherwise, side pickup. I went back to an immersion chiller because they're not fussy, they don't clog, they clean easy. I put a whirlpool port in my kettle and got a pump so I don't have to try and stir to do it. Now I whirlpool while chilling, cuts my chilling time down to 10 minutes, and then I pull the IC out and keep whirlpooling. Any kind of obstruction in the kettle will interrupt a good whirlpool, and isn't that what a hop blocker is?
Whirlpool for 10-15 more minutes, let it settle for 15 to 30 minutes. The junk that is down there is not all hops, a lot of it is cold break material. So far I have not managed to get that stuff to stay in the middle, but it doesn't hurt the beer. So what if a little hops gets into your fermenter? If you don't have a plate chiller to clog, no big deal.
Everyone's system and needs are different, just thought I'd pass on my experience.
