The main thing is to not have a pressure point that will effectively cut the aluminium tube with the harder steel bolt. Aluminium does not fare well against vibration and metal fatigue. The steel u-bolt will cut thru the aluminium tube after a time of hard use. Rubber is not enough protection. datz510 uses steel tubing to spread the stress and protect the inferior Al tubing. My preference is to just use a more resilient tube like Steel 4130 Chromium Molybdenum tubing for the frame. This is what racing bicycles, cars, karts and motorcycles as well as aircraft have used for a long time. Buy a frame that gives you more chance to last a long time, if you want to safely use the bike much.