What are hydraulic bends are they the same as compression or is it the same as crush?

i remember when i first starting modding my car .. i called just about every muffler shop and asked them .. would this work .. do yall have mandrel . how much mroe restrictive would it be ... ... its prety much like this ... from worse to best ....
crushed compression mandreal ... hydraulic is in the middle with compresion . but if it is for exhaust just don't get crushed.