As much as my 5mo loves this ball I can't give it any lower than a 5 star review even though there is room for improvement (as I will detail below). The ball has ten different "nubs" on it with different textures around them and my baby LOVES chomping on them. The nubs are each about the width of my thumb which is perfect for him as it is my thumb he would otherwise be chomping on (or his own fist). A drool bib is a good idea to have on babies at this stage as the gnawing on stuff tends to produce a LOT of slobber.
Please note the ball is SURFACE CLEAN ONLY! Because of the twisting apart (where it makes a ratcheting sound that baby likes and isn't too obnoxiously loud like some other toys, it is also a quiet rattle when shaken), water CAN get into it if immersed (doesn't seem to be letting too much drool in though). One reviewer claims that it smells terrible, I have a VERY sensitive nose and ours doesn't smell after about a month of constant use (it is baby's favorite inanimate object, so much so that we just purchased a 2nd one to have one for home and one for car/out & about). A commenter asked another reviewer and didn't get a response - yes, it is made in China.
As for improvement, one annoying thing is that there is no way to secure it to prevent it from hitting the floor when baby drops it (which babies love to do even when they DO have coordination enough to hold onto something). I solved this personally by putting a small hair elastic around it(fits between the ratchety part and the nubs so it still twists), then using various things such as pacifier clips and link rings through that to secure it to baby carrier or high chair at a restaurant. Having a way to tether the thing with those linking rings would be a MAJOR improvement IMO - and could be achieved by redoing the mold so that one (or two) of the nubs has a hole through it that a holder can go through. It could also be improved by having some gel inside to stay cold after being in the fridge - could be cool to even just have that in SOME of the nubs instead of all of them as I bet babies would LOVE to compare the different temperatures in their mouths (and that also lets parents know if it's worth keeping it in the fridge, if baby doesn't seem to prefer the cold nubs over the regular ones). If there was a way to allow it to come apart so it COULD be immersed and washed thoroughly that would also be an improvement particularly for the more germphobic among us. I get around this myself by only immersing it half at a time and being careful not to get the center split into the water, surface-cleaning that part afterward, but I'd love to be able to like press-and-twist like a pill bottle to get it to open and be able to drop it into a dishwasher or at least a dishbin of soapy water. I wouldn't trade the ratcheting sound and such for that, though, as my son gets a lot of enjoyment from that. If that is particularly a big issue for you, it seems there are other one-piece products on the market that may suit you better.
Oh, and we call ours "the Nom Ball" (as in nom-nom-nom - current parlance for the act of chewing on something). It's the for-nomin'-on in our house (say it fast, it's a very bad pun)