Agree that these filters clean up just fine. Give them a good wash to get the trub off when you're done using them (they are not so delicate that they disintigrate when you hit them with a sponge), and then spray them down with sanitizer before you filter and you are good to go.
I wouldn't use these (or other plastic equipment not specifically rated for high heat, e.g. a plastic fermenting bucket) with boiling or near-boiling wort. Do you pour boiling wort straight into your fermenting bucket? I do a full boil and chill in the kettle to pitching temps and then pour into the fermenting bucket with the filter set on top. I guess if your process involves pouring boiling wort into a fermenting bucket with ice water in it to chill, you could instead just add the ice water to the kettle before you dump into the fermenter? Whatever your process it might be beneficial to chill the wort before you filter to get the "cold break" out of solution so as much of that as possible will be filtered out.
As to the 100 micron filter you could definitely use it if you're willing to stop your pour numerous times to clean out the filter. Keep in mind that 100 microns is very fine, so it's not like huge chunks are making it into your wort. As you'll see here poptarts is getting results he's happy with using three nested filters (600/400/200) and I've been happy using just the 600 to minimize the amount of times I have to stop my pour to clean out the filter. Yes, some trub still goes into the fermenter (obviously more for me than for poptarts), but either way it's
way less than letting the trub settle and doing a careful pour.
Based on poptarts' experience I'd advise anyone interested in using the filters to go ahead and order the 600, 400 and 200. They're cheap and you can always use fewer (as I do) if you find they're getting gunked up more than you care to deal with. I can say that using even just the 600 totally changed the character of the sediment left in my fermenter after racking off to a much more pure looking (and significantly smaller) yeast cake. That plus less sediment in the bottles keeps me doing it the way I'm doing it. Having said that, lots of veteran brewers at HBT who make much better beer than me don't filter at all, and rely on whirlpooling, a careful pour into the fermenter, careful racking, and sometimes cold crashing, to clear up their beers. So it really is just a matter of preference and weighing the inconvenience of potentially having to stop and clean out a filter mid-pour with the convenience of having less sediment in your fermenter, and hopefully losing less beer when you rack off as a result.
Hope others who try these out will post back here, I'd be interested to hear if others are having success with not having to clean out nested filters multiple times!
Also, for reference here's an older thread where various post-boil filtering options are discussed (and where I first learned about these US Plastics filters):
https://www.homebrewtalk.com/f11/strainers-5-gallon-buckets-128094/