Thank you Ouryve, I have only used the coverstitch on my Bernina in the shop and when I got it home took the conversion part off and put it away, so this really will be an experiment thus my getting something in knit fabric that I can chop up and play with to make sure it is working properly, and I can get used to how it stitches and also to be careful at the end of a run as if I am not careful the coverstitching will unravel all too quickly. I do not have spare decent fabric so I need to get this right first time. Also I normally use a three thread overlock, so going back to a four thread and seeing how that behaves on knit fabric again will be a first, and yes I have a differential setting.
I am just so lucky in having these two Berninas, the smaller one which I tend to use for day to day stuff I bought three weeks before my daughter's wedding as my then Elna was playing up big time, and I needed everything finished. I was happy with that machine, and then an elderly friend of mine was rather envious of my new acquisition - she had a very old Bernina square shaped base overlocker and no amount of trying to adjust this would stop it from continuously breaking the thread, so it was dispatched to a place where they refurbish old machines and send them to Africa. My friend was then left without an overlocker and bless her she thought that her age 80+ she could not justify spending a tidy amount on a new Bernina overlocker, but fate stepped in. The shop I bought my little overlocker in was selling off the top of the range mighty big Bernina overlocker/coverstitcher it had only be used for demonstrations, and I just happened to be in the right place at the right time, and thus I sold my little overlocker to my friend. Sadly this friend became terminally ill and she wanted me to have this back, and it wasn't until I picked it up that I realised that she had never used it - such a shame, so that is how I have two machines. The larger of the two machines does a lot more than just overlocking and coverstitching and of course I have yet to try those out even though I have had this machine for a long time.
Now yesterday whilst in the charity shop there was another elderly lady who mentioned she had a newish Bernina sewing machine, and she was surprised that I wanted some knit fabric to play with on the machine, and I said I always do a test run on seams, buttonholes etc. on anything I sew, she obviously doesn't. I learnt the hard way back when I bought my Bernina Artista and did around 21 test buttonholes, - 21 because they were not right, and the reason was because the sensor in the actual machine up by the needle was covered in dust/debris but I did not know that then. so now I always make sure when using that machine that it is clean and clear of debris before any buttonhole test is made and then when I am actually sewing the buttonholes.
I am hoping that by using the overlocker to assemble the garment will indeed be much quicker than using the sewing machine - but only time will tell, and also whether I like the finished look, both on the main seams and the coverstitching on the hems.