dang new to me i been useing them since from 2002,never a problem as long as the otor is built right you should be ok..i mean the only valve set i really stay away from is supertech,,but everyone has a story..i have used ferrea in many many i love them but i use rev more for the price.i always brand new ferrea locks on the heads NEVER reuse old locks when useing new valves thats where most go wrong..or they use stock retainers with them...its up to you if ya feel better getting ferrea do they are a great valve set..go with the 6000