My 4 cents (this is a bit long)
the necklace/long hose reason: an octo is there for emergencies, to be able to end a dive - does it really matter much breathing from e.g. a R195 vs. G260 for a few minutes?
This I would answer in 2 pieces:
It does matter, within rec warm water limits OOA/G situations sneak up on you, besides being stressful mentally, they can be also physically
30-40m on Air is still “rec”; and gas density there is quite high, and close to comfortable limits.
If you are hyperventilating because of fighting current or panic due to OOA, that get you to a “risk” zone, not full risk but let’s call it “yellow light”: CO2 offloading
Now saying that is no implication that an r190/5 has poor or inadequate performance, it’s kinda fancy actually (far better than my 1st kit), and I believe in its “peak performance lifespan” (seat wear amd all, is almost on par with the 260
After buying my first kit to go on a liveabord (rec stuff only) I had a couple of shore dives check it before I’m there for a week
I basically “party crashed” someone’s rescue course in Hurgadah
First dive went alright, 2nd also good all the way to the turnaround, one minute I was 110 bar, the literal next 30, I am relatively calm still and I tell the guide/instructor
By the time he handed me his Octo (on a 110cm hose) I was at 0bar (very close)
I was on his left side; I think he also wanted out ASAP, so was finning like carzy
So we ended up being in a situation where he is dragging me by the mouthpiece, me trying to catch up, stressing, momentarily dropping his octo, chugging a bit of water, getting the octo again, calming down, asking him to go slowly, and safe at shore
(And they got a live victim to practice on for their class)
At shore we figured it was my HP hose transmitter interfaces (I didn’t spool it) that leaked
Got onto the boat fine, had fun, all good.
But if this happened to me at Canyon (Dahab) I’m quite sure it would have turned nasty
Since then I just upgraded the hose length of my octo, I don’t imagine anyone would like being dragged or that close up, I still have that 1st kit and use it sometimes, it has 2 identical (except for color) downstream regs (cressi compact XS) that frail in performance compared to my g260s; but they are matching, I don’t lose any performance I donate, I value my buddy’s life as much as mine
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Nothing is stupid, some “schools” prefer downstream octos as they are better at handling IP creeps to save yourself from bursting hoses; some just prefer them because of how simple they are, some really dislike them.
We can share our thoughts to council OP and they’ll make the final call
I am for longhose / necklace in any diving situation, good habits die hard
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the save a dive/Service kit reason: don't know how good the OPs technical knowledge is. For me it would not be a real difference, I can neither Service nor repair a regulator, beside of changing a mouth piece.
A service kit (esp for 2nd stages as they need much less complex tools to deal with) can be the difference between someone on the dive boat (or that dive shop at the destination that isn’t a dealer for this brand but certainly can service it) being able to fix it for you or not
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the one reg fails on a trip, use the other Main reg-reason: is it diving with only one reg, without an octo then?
Mabe you can rent an cheap octo and it becomes your octo, you still have a nice primary
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The switch between regs as primary/secondary between octo Id say is the biggest advantage; really elongates the “peak performance” life, regardless of reg design
My old s600 has seen the most dives and beating but is going strong and will probably outlast all the others 
