I used Monojects a number of years ago and was frustrated by the varying amount of insulin that "hid" in the cone (making the dose larger than it should have been). I then converted to Terumos (following
@Marje and Gracie's advice), and they were indeed really good (unfortunately now discontinued). I tried every brand after that and most were terrible. So I went back to Monojects and discovered that they had changed manufacturers and were drastically improved. I used them until Rusty died in July 2018 (measuring his tiny dose with calipers).
If you are interested in the "original problem" with Monojects, check out the Google doc I prepared many years ago!:
https://docs.google.com/document/d/18Sy-_ED9Vi_119OVGEF71zZ0PM6op2R_07oz578xaWU/edit