He's not asking to compare Racktime racks to steel racks, he wants help comparing 2 Racktime racks...

Looking at the Tour-it, I think it would support panniers better than the Add-it thanks to the third vertical tube. The platform also looks wider on the Tour-it, which is nice for strapping stuff on it, but can't say for sure without measurements... In case you would care, the Tour-it also has pump pegs for a mini-pump (I wouldn't care).

A potential downside to the Tour-it lower rails is the length: you can only install panniers with a hook distance (outside-outside) of up to 165mm, which is not a lot. My Ortlieb currently needs 220mm of space to hang them and that's not at the widest (most stable, bag friendly) setting at all. The widest setting possible on my Ortlieb Backpacker Classic panniers would need about 275mm. No data for the Add-it though, so difficult to compare, but the pictures do give the impression that there's more space on the lower rail on the Add-it.