Soooo… I took the plunge and did a short hop from MEL to SYD!
Yup, the aircraft is nice and new and seems all very ‘fresh’.
Positives… extraordinarily generous recline! There’s a good 5-6 inch recline which makes the seat very comfortable. Seat fabric… no complains there, it was fine, not overly ‘scratchy’ as mentioned by some pax. Air vents worked well and the overhead bins are indeed large. The extendable headrests work well, staying in position, and go up quite high.
Negatives… I read above that there was no noticeable difference in seat width and I thought ‘how is that possible being an airbus?’. Unfortunately the observation is correct… in fact worse… the seat is/feels narrower than the 737! I was trying to work out how… perhaps the aisles are slightly wider? (And i was not in the last row or anything where seats can sometimes be narrower than the others.)
Despite the slimline design, there is no extra knee room… except when reclined. In fact it might be a bit worse. On the 737 my knees touch the literature pocket when the magazine and headphones are stowed there. On the a321 my knees touched without the magazine there!

And right by your shins is a hard metal bar running along the bottom of the literature pocket.
When reclined however, there was significantly more leg and shin room. MEL-SYD maybe not a winner, but MEL-DPS would be.
Oh, and something that
JohnK has mentioned with SQ… the curve of the seats seems to try and give a degree or two of partial recline even when the seat is fully upright. It’s not that comfortable
The windows… mentioned above… seem VERY small.
WC ratio wasn’t a problem, only a few pax even used them for the short flight.
There were indeed 5 crew. 2 serving in J and three in Y. Two crew started with a trolley at the front of Y and a third crew started at around row 26, working their way to the rear.
As for the overhead bins… not a single passenger put their bag in sideways and upright! I don’t think many people could actually see the signs inside the lockers. But despite multiple announcements from the crew, no one actually did it. Perhaps if the flight had been full late arriving pax might have rearranged the bags? What most pax did hiwever was put their bag in as normal, and then place their smaller item on top.
One annoying thing… the entertainment system has been ‘fixed’/updated so you can no longer fast forward the advertisements

My flight on the 737 last week you could still do that, but on the 321 no deal
Plane… yes, nice and new. Seat 10/10 when reclined, 6/10 when not. If you are shorted than 6’1, the seat probably gets a 8/10. Service pattern and crew, same same (really good). IFE 8/10 because you can’t fast forward!
The test will really be a full flight to Bali, or longer.