Also have an Aeron. I first used one at a job in 2001. They get real cheap after each downturn in the market as companies offload them by the dozens.
This year I’ve been trying to use a standing desk more than half my coding time though gradually increasing it as my back adjusts to the different position. Posture has improved tons.
I tried the kneeling chair and just couldn’t make it comfortable for me. I’m going to return it and try the Markus.
I love my Embody. Definitely a pricy chair but it paid for itself in short order. It’s really comfortable and configurable to just youself.
Which one did you get Barry? Is it height adjustable? In what way are you finding it uncomfortable?
I got the DRAGONN Ergonomic kneeling chair from Amazon. Just put too much pressure on my knees after a while. I didn’t actually order the Markus yet though. I decided I’d give the bungee chair from the container store a shot first. Should be here next week.
Ah that means the seat is too high - lower it until it feels (a lot) better on the knees - there should be very little pressure on the knees 
That was actually at its lowest. It was fine at first but after an hour or so it just wasn’t working for me.
I was also a little too big for the chair.
Just had a look on Amazon, and the angle of the seat on the DRAGONN doesn’t look great tbh - it slopes too much. By contrast if you look at this one:
https://www.amazon.com/dp/B00429Q38I/ref=psdc_13749671_t4_B073ZN7B52
And this one:
You can see that the seats are more horizontal - which means they will support your weight on your buttocks better. On mine (pic in first post) I’d say 95% of the weight is on my buttocks with 5% on the knees - or at least that’s what it feels like 
This is the chair I use.
I was starting to get back and neck pain about 8 years ago and this chair basically changed my life. It feels invisible. I never feel it is pressuring me.
PS: I had no idea it is this expensive. Long story short: I bought it at production price because a company imported about thirty units for another company which went bankrupt. So the intermediate company was selling it at cost - basically half of the price on the website. But to be fair, most of us spend one third of our days on those chairs - so the investment is worth it. I have had mine for 8 years and it is still going strong.