I would say avoid if possible. Birth defects are quite common if you inbreed too much, Usually in the spine area. You end up with short fish
that have twisted spines. Ive bought in large batches of fry in the past to grow on so I can pick out a few good quality fish to add to my breeding stock and its quite obvious when they have been in bred due to deformaties sadly. Its something I dont do myself. I make sure when I'm buying in new strains that I buy from several different suppliers up and down the country and also local shops if they can get them in. Strong genetics tend to mean very healthy fish that go on to have healthy young.