Njanear is correct. Most BUIS have windage adjustment, but no elevation adjustment. Why do you need elevation adjustment for a BACK UP Iron Sight? It is just one more thing to get screwed up.
Are you wanting a flip-up or a fixed BUIS? I really like the Tryo flip-ups. BUilt like a tank. Windage adjustment knob won't get accidentally "adjusted". Very fast to deploy.
For a fixed BUIS I love the LaRue. Doesn't take up too much space. Has adjustable quick release lever. QD lever is on the right side so it does not interfere with the charging handle.