It will last the same amount of time (maybe a little longer), will feel even cleaner because you are bypassing the early stages of the digestive system, and will hit you HARD and NICE!!!
If an average pill weighs 0.5g, and you compare its effects to exactly 0.5g of Molly, the Molly will hit you at least twice as hard because most pills are only 50% MDMA (if that). But if you plug something, about twice as much is absorbed. That's where I got the 4x from. And keep in mind that's a minimum. I don't know what pills you're used to taking or how many at once, so I won't give you any specific comparisons re: how much to take. But if you've taken crystal before, and usually take X amount orally, take 'half of X' amount rectally the first time you plug.