Thank you for your replies everyone.
I'm a regular user of ScotlandsPeople - wish they did some bulk discount, or offered 5 free credits for every 50 you buy or something, or even a sub instead of pay as you go! I have more than 500 records in my saved searches, and at at least 6 credits each that's around ...... mumble mumble....a lot. The earliest being a will from the 1590s that's almost unreadable. I also use our local FamilySearch affiliate library to browse records. I trawled through a couple of decades of 17th century Edinburgh baptisms (it's about 100 images each year) as there was no way I could afford to buy that many records and I was mostly looking for sponsors to help work out kith and kin. So I'm very familiar with ScotlandsPeople.
My question in my first post was whether accessing these three particular record sets via Ancestry is working for others.