I still use my 11 year old Thinkpad together with my newer Thinkpad. I use both laptops alternately. My productivity does not increase when i use the newer one

I still use my 11 year old Thinkpad together with my newer Thinkpad. I use both laptops alternately. My productivity does not increase when i use the newer one. That's said my extra 20 inch monitor helps me to visualize.