I have one. It is the Kensington Footrest
It is nice, but I dislike the lock being at the bottom as it is easy to accidentally unlock with your foot.
The foot rest is a game changer for me personally. I’m 5’9” and with my chair leaning back my feet didn’t touch the ground. This fixed that, plus it is really nice and cushy. I got one used for like $25 on amazon. It looks white in the pics but the one I got was gray. I spray painted it white to match my setup.
Kensington Comfort Memory Foam Adjustable Footrest (K56144USF) https://www.amazon.com/dp/B004UQ40IS/ref=cm_sw_r_cp_api_i_6T31BbK1AS5TA
Here's the footrest. The memory foam feels amazing, especially during long sessions. You can also adjust the angle of the footrest very easily to get that perfect fit. Definitely would recommend it.
Edit: Posted incorrect link previously
If you can’t adjust the desk, you can rest your feet on something like this or a half cylinder cushion.
Late to the party, but do you have a footrest? All chairs are uncomfortable to me unless I have a footrest. I have this Kensington one under both my desks, and a cheap Amazon Basic one under my workbench. Kensington Foot Rest (Amazon)
Without a footrest I get pain under my legs where they meet the edge of the chair. (I have Titans now, but similar in design and I suspect firmness to the Hero) 6'3", 240 lbs, muscular. I have lower back issues, which these types of chairs deal with amazingly.
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Edit: Sorry, realized you were in the UK. Here is theAmazon UK link for metric folks.
Yeah, it's a foot rest! Bought it from Amazon. Get's kinda smelly LOL
I have the same one, I got it from Amazon. Here you go: https://www.amazon.com/gp/product/B004UQ40IS/
Yeah it's an adjustable footrest: https://www.amazon.com/Kensington-SoleMate-Adjustable-Footrest-K56144USF/dp/B004UQ40IS
I use this one. Fucking love it, so comfortable. https://www.amazon.com/Kensington-SoleMate-Adjustable-Footrest-K56144USF/dp/B004UQ40IS/ref=sr_1_17?ie=UTF8&qid=1478875482&sr=8-17-spons&keywords=foot+rest&psc=1