I don’t think your missing anything, I’m in the process of installing one myself after have an impeller come apart on me on a
passage.
Of course it required disassembly of the heat exchanger to get all the impeller
parts, in an anchorage, with no access to any
parts and hadn’t checked in with Immigration yet either, and Seatow wasn’t an option. A concern was if a piece got through and plugged the one hole water flows though in the
exhaust elbow, I’ve heard of that, but thankfully it didn’t happen to me.
The strainer I found is a lot larger though. I believe I’m going to hang it on the side of my heat exchanger “Yanmar”
Of course once the strainer is installed if an impeller ever comes apart again, I’ll just open the strainer and remove it, no disassembly of the heat ex required.