I have just purchased an ITR Thread Boss and have noticed that when the thread is pulled out of the unit, when let go, it will retreat back into the unit much like a spring loaded tape measure. That makes it impractical for effects when you need it at a certain length and you don't want to be pulling on it to keep it from going back into the unit. Am I missing something here or what do I need to do.

You need either to 'anchor' it between or around your fingers in some way or maybe have a seperate line of just IT.

I thought thread boss was slow retraction.
Is it worth buying? if so does anyoneknow where I can get one cheaply.

You're not missing anything - that's the way they work. It's also the way the Spider pen works. You can use it for effects where you need a horizontal fixed thread, but for effects where you need a non-retractable length of thread, you need to use a piece of IT without the reel. In other words, if you need a certain length for a certain trick, you don't use the Boss. Different methods for different effects. I hope this makes sense.

Jim

You could anchor it to a table in front of you and then float things on it without worrying about it retracting.