When we purchased our boat, the thru hulls were plain open mushroom type. I had very frequent problems with grass or other plant material being pulled into the thru hull. Some would end up in the strainer basket, but most would lodge in the ell at the strainer inlet, or would jam up in the riser. The strainer basket was easy enough to remedy, just clean the basket. The times with the obstruction in the riser were always a pain. I had to pull the strainer and the inlet hose to clear the obstruction. If enough stuff jammed the inlet, the valve had to be opened and a ram shoved down thru while keeping a rag wrapped to mitigate water ingress.
I finally tired of the drill, and added the exterior screens. I screwed them on, using bronze screws, one of which was a thru bolt to maintain bonding conduction. The screens were a very welcome improvement that about eliminated the blockage problem. The only time now that I have a problem is toward the end of bottom paint life, and the screens tend to get shelled up. I'm typically under the boat once or twice during that interval, so a bit of attention with an awl is enough to keep them clear. If I had it to do again, I'd use the hinged screens- easier to maintain. But the screwed on ones have been quite effective.
Worth mentioning is that I did not screen the inlet for the stabilizer cooling or the seawater pump at the bow. The stabilizer's really only run under way, so grass isn't an issue, and the seawater washdown is run infrequently enough that it's never pulled grass into the thru hull.