Welcome to the Quilting Board!
these are really practical, and there are some really cute ones, but one has to be organized enough to throw the threads into the bag...I have tile floors and it's much too easy to throw it on the floor (impersonate eleanor burns!) then sweep it all up later!!!
I have a thread catcher and love it as so much easier for the pincushion and catcher combined!
nice to take with you on sew days, retreats etc.