My last service had the O2 bears. They were great for small kids that just needed blow-by. I would use a mask for neb treatments. As Vent said, the neb treatment does not work well on blow-by.
I always let the kids keep the bear, when we dropped them off.
I did have a Downs child that had to have neb treatments every day. He would not allow a mask near his face and would not use a mouth piece. I gave mom the neb attachment for the bear. She called a few weeks later and was very thankful for it. She said that he would take his neb treatments without a problem now and had not been back to the ED since, because he was using them regularly. My captain told her that she could come pick up a new one, any time the old one started to get ragged out. She was very happy and that little boy just loved that yellow bear!!