Flobear regarding blind hemming, it does take a bit of getting used to, but the best thread I have found for using this method is Madeira Monofil No.60 this really is an ultra fine filiment and comes in two colours clear or smoke. Now do not use the Madeira Monofil No.40 that is far too thick.
I used the No.60 on some Thai silk lining and it is lovely.
Now a very long time ago there was something I think called Perilusta and that is what they were using for blind hemming and at that time it only came in a thickish thread and was horrible to use. This new Madeira Monofil is gossamer like and comes on a reel a bit like the Sylko used to come in, and it holds 1000mtrs. (whereas the No.40 reel only holds 500mtrs).
Yes this Madeira is not easy to find, so I doubt very much any local thread place would stock this so it means looking further afield, but as you can see one reel of each is going to last you a very long time.
Incidentally I found that the instruction manual for the 830 Record is really clearly laid out and so easy to follow how to do things. I have inherited my mothers 830 Record and this is my main go to machine these days as it had not been used too much, like all Berninas they are a joy to sew with, and when this first came to me I added a few extra feet, and one of those was the Edgestitch Foot No.10. You can probably still get some of the old style feet and if you want to may I recommend using Bernina's own warehouse down in Cardiff - the ladies there are so very helpful and it is always a quick dispatch, and they will ensure you get the right foot for your particular machine. The Cardiff warehouse phone number is 029 2079 2079 and two of the ladies down there are Rachel and Jackie - they really do go the extra mile for you.
Also when I inherited my machine, at the time I came across some Sewing Leaflets produced by Bernina possibly for a later machine than my 830 Record, but I scoured various machine shops and the internet looking for these leaflets and have found them extremely useful, they comprised a set of 24 and they are called Bernina Sewing Service and cover all the feet and their uses, there are a few for the overlocker attachments. Then I came across something else produced by Bernina and these were called Bernina Collection - I do not know how many they produced as I only have a few but again lots of lovely ideas showing you how to use your machine to its full potential. I just need to find the time to stop and play.
By the way Bernina seem to have had a promotion going on through the year and have been offering foot of the month and often these have been reduced by a fair amount, so it is worth going and looking from time to time to see what they are offering.
www.bernina.com and this is their own website.