It's a great idea - the shape and all is good.  However this is made out of bathing suit material - super stretchy.  My 4 year old was able to easily slip her thumb out of the thumbster at night (or any other time) to suck her thumb.  The velcro is so cheap that it didn't last a week before it stopped working.  A note on the velcro - it's very easy for a child to undo.  If this were made from woven cotton and had a button on the wristband, it would actually work.  Since it isn't, it was just something I wasted money on before finding a solution that actually worked.