What is the opinion of Reddit about the
Titan T-3 Series HD Power Rack with Dip Bars Squat Deadlift Lift Cage Cross fit?

Honestly, for used gear, them asking 80% of the paid-new price is really pretty high, unless it’s like-new and exactly what you want.

The $550 T-3 rack is $480 on Amazon, shipped (before tax). So unless the tax rate is over 10%, you can get it a bit cheaper than it’s listed for here.
https://www.amazon.com/Titan-Power-Squat-Deadlift-cross/dp/B00PTBE40C

So I’d say no on this one, as you’re over 80% of the like-new price.