so, somehow I ended up with a speed feed 450 as an attempt for blount to get me a working trimmer head, so I figured I would share my experience, the good, the bad, and the fugly. so, as a plus, unlike the 2 other heads they sent me that were supposed to fit my trimmer, this one actually fit the shaft. unlike what I had heard of and saw of people struggling with the echo heads, this one seemed to come apart and go back together rather easily. the spool seems like it will hold much more than the ~10 feet listed on the package, I see more like 18-20 feet. it seems well built, but it is quite heavy, more on that in the "bad/fugly" sections. loading it is indeed quick. changing the bushing was uneventful, but the cap/turn knob got in the way a bit of screwing it onto the trimmer. thus started the problems. the bad: my first problem was it kept flying off when I tried to start the trimmer (I've had 2 other heads on this trimmer, installed equally tight on this trimmer with no problem). the fugly: it fell off several more times, even after using it (which usually tightens it more), and it never seemed to tighten as stiffly as the other heads, even when I stuck a pin in the "head hold" hole. then I noticed when I shut off the trimmer, it actually wound the string back in (one time all the way back into the head). now, I must say, my trimmer has no clutch, but blount should have thought of this, IMO. I blame the sheer mass of the head combined with lack of clutch for both issues, along with it somehow not wanting to tighten down (for it not staying on). it frustrated me to the point where I gave up trimming for the day with that head, after less than a full property. did I mention it was heavy? so much so it made my trimmer bog down a bit.