Mu bushes are about 4 - 4.5 feet tall. Height as well as how well they produce depends on a lot of things. Late freezes have killed one years crop, this years was weak but nothing terrible. You have to dedicate enough area for the roots to spread as well. Like any plant the soil as well as the variety dictate how well they will do. I buy sulfur chips in 20lb bags and spread them every other year at least. I've lost some plants but most were because either I didn't water them enough during dry spells or I bought too small or bare root plants. The latter have to have perfect soil to get started. That's why I've just bitten the bullet and gone for 2 gallon or larger than plants.
The key is that after you get them established there are very few bugs that bother them and maintenance is very easy. Water, Fertilize, pick, then prune in winter, repeat. IF japanese beetles hit (usually late in the picking season) a little neem oil solves that.
OH - Almost forgot - There is competition - Birds and Deer. I use netting which is a pain but have that down to routine now. (Birds hate me and tell me so when they see me go pick.) Of course nothings better than free wild blackberries and black raspberries.
