I'd sat in Aerons in workplaces, so I bought a second-hand one on Craiglist for about 50% of list price. It's still going strong 5 years later.
Be aware of the options. Aerons come with one of two forms of back brace (or neither) and in three sizes, for instance.
I have a Hermann Miller Mirra 2, bought from https://studiomodern.co.uk in the UK. The Aeron is a 'design classic', so hasn't been iterated upon much. The Mirra has benefited from the experience though.
Also expect to spend a little time setting it up to start with, and then tweaking it until it's just right.
Have had mine for 6+ years now and it's outlived pretty much everything in my home office, save for a Dell U2713HM, which is still such a nice allrounder (27" 1440p IPS).
Also, I would recommend ignoring Dell's dual-monitor stand for these monitors (Dell MDS14 Dual Monitor Stand). It doesn't allow for the monitors to be angled inward very much at all, so the monitors are mostly parallel with each other.
In my case, I spent some time trying to optimize the price - finding that one desperate Aeron seller who'll let it go for $250. This turned out to be a waste of time. When I got a second one (rarely used) for another room, I just paid what appeared to be the going CL rate.
I had to replace the seat after a few years, but that's a standard part that you can order from Herman-Miller. I also replaced the casters last year for gel wheels that don't leave little marks on my floor (third party part in that case). I use the chair a lot and I have no complaints.
I sit on a Steelcase Leap at work (ordered new), and for me, it's not quite as good. But it's a small difference.