I do not have a problem with flex takeoffs when they are within my comfort level. Normally there are quite a few options on the final paperwork. I like to look for a certain cushion (around 4500kg/10,000lbs) between the performance limit weight (associated with a particular flex temperature) and the actual takeoff weight. I'll ask whoever is reading the printout to look for that cushion, however there are scenarios where you are normally max'd out (BOM). In those cases one simply remains aware of such conditions.