I had a Balvar 2.5-8 on my first custom rifle I had built in 1957. It used the external adjustable mounts as made by Kuharsky, in Erie, Pa. It was a fine scope in it's day, and I thought at the time that it was the best. I sure liked it and shot a lot of game with it back then. But, it was 1950's technology, and there have been significant improvements in glass and coatings over the years, so there are probably better scopes made today. I personally wouldn't have a problem buying and using a Balvar today, since it was good back then, it will be good today. But, it won't equal the best scopes available today.
Martyn