I travel KLM quite a bit and usually with an A45/S25 or a WF/S25 and I've never been hassled in 20 years except the time I got exit row on an intra-EU and found out nothing under the seats, no bag on your lap no matter how small! Wasn't a biggie, both bags went into the overhead, but I was totally unprepared to not have my small flight ditty bag ... what a whiner i am. anyway ... oh, right, we were talking about you!
I'd say if the S25 worked, the A30 definitely will too
*IF*, the A30 works with your packing and travel style; it's got no internal org, etc so it's a totally different experience than the S25. For me, the Aeronauts are only "bag no 2" as I'm a two-bag traveller so I always have another personal item bag (usually a lightly packed S25 or Pilot - this becomes my day pack too)
If you still want the S25 org, then the Synik 30 would be the no-brainer choice or, for even more room, the Brain Bag especially since it has the side compression straps for expandability/shrinkability and you can easily put an A45 PCBP in one of the two main compartments ... that way if you're ever hassled just pull out the PCBP and cinch down the BB, plus you have the PCBP for a day pack.
Anyway, others will have better advice because, as you can tell, I don't worry much about carry-on requirements; mostly because I fly major airlines vs economy (i.e. Delta vs Ryanair, Spiritair - although i do fly Southwest a LOT!) and in 20+ years of pretty regular flying (in NA, EU, APAC; and 10 of those years non-rev at an airline!), I've just never been once asked about my carry-on size. That said, I do smart stuff like wear my A45 as a shoulder bag for the gate and boarding, etc and, just like the cops, if you have a big oversized brightly colored bag ... well those are the people I usually try to line up behind
