What is Reddit's opinion of StarTech.com 2U Sliding Server Rack Mount Shelf - 20 to 30in Adjustable Mounting Depth - Vented - 50lb - Heavy Duty Universal 19” Rack Shelf for Equipment Rack - 24in Deep (UNISLDSHF19)?
From 3.5 billion Reddit comments

By popularity on Reddit, this product is:

The bottom printer has a slide-out StarTech and the top printer has Navi 1u.

Amazon:

StarTech.com 2U Sliding Server Rack Mount Shelf - Adjustable Mounting Depth - Vented - 50lb - Heavy Duty Universal 19" Rack Shelf for Equipment Rack (UNISLDSHF19) https://www.amazon.com/dp/B003AVPV0U/ref=cm_sw_r_cp_api_i_x4T-Db1BV6BYV

NavePoint 1U 19-Inch Fixed 4-Post Rack Mount Server Shelf with Adjustable Depth from 18-34 Inch Black https://www.amazon.com/dp/B00LT6432U/ref=cm_sw_r_cp_api_i_TWT-DbAX0KV0V

The printer can’t slide out yet using the shelf as the filament is mounted on the cross beam like this .

I’m working on a rack mountable filament holder so once I get it the printer should slide out correctly. (Clearance was previously measured)

The bottom printer has a slide-out StarTech and the top printer has Navi 1u.

Amazon:

NavePoint 1U 19-Inch Fixed 4-Post Rack Mount Server Shelf with Adjustable Depth from 18-34 Inch Black https://www.amazon.com/dp/B00LT6432U/ref=cm_sw_r_cp_api_i_TWT-DbAX0KV0V

$100 - $200

< $50

$200 - $300