Personally would'nt bother with one as I still found lumps which made me gag. Go to tesco and get a blue stripey hand blend for about £5 makes wonderfully smooth shakes, add ice to make them lovely and cold and frothy. I know some people love the shakers but personally I just can't get on with them.
I got one awhile ago form Argos. I think it was a maximuscle make and cost about £5. Never used it though and my brother uses it instead to mix his protein shakes. I'd imagine that they wouldnt be very good. I'd suggest what poppy reccomended, hand blenders are awesome or have the tetras if you need to have your CD meal when you're out and about.
i always have my shaker with me. i've started drinking my shakes warm though and i can't use it for that. but it's always handy. not quite as nice as when blended but i think i've only blended once so i don't know what i'm missing