We followed the assembly instructions and they frequently sink to the floor; like the hydraulics don't work correctly.  I've wrote a question twice asking if there is a way to lock it in place and have yet to get an answer, which is annoying.  The whole reason we bought new chairs was that our chairs had gotten old (2 or 3 years old) they kept sinking and we got tired of basically being on the floor.  But these are new chairs; so I'm not super happy.  Other than that the chairs are what they say they are.