I have both and I like the 250EX but use the 255EXT more mainly I like the memory part have it set for most of the welding I do just go thru the number till I get what I want and weld, no turning knobs or moving switches for the settings it is a little more money but it is worth it. If you are switching back and forth from thick aluminum to thin or to steel just have the preset number for what you want. I have used all the different wave forms and used Advance Square with Advance AC Pulse for some jobs it is different. Just welded a cast aluminum water pump with the 255EXT that broke over the winter and froze and blow the bottom out of it.
Everlast PowerTig 325EXT (Canada)
Everlast Power I Mig 250 (Canada)
Everlast PowerPlasma 80S (Canada)
Everlast PowerCool W300 (Canada)
Everlast PowerMTS 250S Fitted with a 30A Spoolgun(Canada)
Miller Dynasty 400 wireless(Canada)
Millermatic 252 plus 30A Spoolgun(Canada)