The stihl FS100 (I think its FS or FX)is a good one. I have had it for about 5 years now. For the first year I ran it with the guard on and I was cool with that. One day it broke and I said I will run it until a rain day came then go get another guard. But in between that time I noticed that I fell in love with the damn guard being off for a number of reasons (easy to get in smaller areas, wider trimming swath, lighter on the front end, ect...). I never run it with the trimmer line too long, just a little longer than the guard allows. I still used that same trimmer today and it runs like a champ. I have taken the guard off all my trimmer now and wont put them back on. I know about the warranty and the trimmer slinging rocks and yadda yadda yadda. I personnally am willing to take that risk. Im not telling you to take off your guard, Im just telling you my experience and maybe this can help you make your decision.
But to answer you question the stihl 100 series is a good trimmer, but not sure how it compares to redmax because stihl is the only trimmer I have.