Out of laziness and having a wife that vapes like no other only bought pre-filled the first 6 months of vaping(wife also would never refill does now).But I did at least save all them carto's and glad I did,definately refilling the way to go for BIGTIME SAVINGS......now refilling is just routine.
Mind you, I had the wrong size /type of needle so I did struggle. My subsequent efforts have been more successful.