You are better served buying a spare dust cover and having a homemade aperture welded to the spare cover. That way, the dust cover is removable, you are assured a strong steel peep sight with a diameter that works best for you, and I bet it would cost the same.
I have used a tech sight on sks. If I remember correctly you had to remove it in order to remove the dust cover for cleaning. So a real pain in shooting corrosive. Also you end up losing the stock sights ability to change range setting. Its a bit busy sight picture You are still going to see the housing where the rear sight was. Finally its made of some sort of pot metal and easy to break when you install it.