Unfortunately I can't give you advice on these two machines. I purchased a used Elna Serger (floor model) a few years ago and it's nice to have in my arsenal for retirement. I have enjoyed having it the half dozen times I used it.
When I did purchase my serger one of the things I noticed was how much noise the machines made. There was quite a difference in the ones I tested. That was a deciding factor for me. I suggest you test both of them and see how comfortable you are with each one. If they are not threaded, get out the instruction manuals and go step by step -- it's good practice!
Happy quilting!