My only order of 25i, I took 1mg nasally, tripped good. 7-10 days later, had to take 4mg nasally for the same effect. Another week later, took 15mg 2C-P orally, and 15mg 2C-P rectally, very minor effect, almost no visuals. I am experienced enough with 2C-P to know that 25i killed my dose. Despite 25i being good visually, though lacking mentally or bodily for me, I will never order it again, due to this tolerance, and it being even more nauseating and headache-inducing the a visually-equivalent dosage of 2Cs. And I really don't go for 2Cs much anymore, as visually-equivalent dosages of 4-sub-Trypts have less tolerance, nausea, no headache, and better body effects and euphoria. Still have yet to find an RC with a decent mental trip unless on heroic doses, bar dissociatives.
Edit: I can trip twice a week with classic psych PEAs on same dose, and 3-4x/week on same dose of trypts. I coulda dealt with the nausea/headache from NBOMe's, but the long tolerance is was made the decision; I will never buy NBOMe's again, just not worth it. Hallucinogens are my fave class, and I like to trip often, something which is impossible with NBOMe's.