I bought two one for the cot and another for the crib (which noah is no longer in!) I was advised not to use them (until baby is 12 months) by the hospital and then by my MW & HV!
I ended up using it around the bottom of the crib (I weaved in and out of the bars) as Noah kept sticking his foot out the bottom & getting it stuck!
I dnt think it would prevent a LO sticking their arms or legs out of a big cot as if they're in the feet to foot position they're arms & legs aren't near it! I still wouldn't use one though until 12 months!
Think the shops sell a lot of things for money more than practicality TBH! I know when I was PG I wanted everything in the room, bumper, quilt, matching lampshade, wallpaper etc! Had I have known you weren't ment to use a bumper I would have bought them! Wish we'd have never even done the nursery out as Noah's never even been in it and we're moving so will only have to do it all again!

But it was one of those things.....I wanted him to have everything proper and nice!
xx