I have two cats, both of which are growing like weeds and definitely do not fit in the same carrier anymore. The fact that these have removable wheels saves my back from carrying two little monsters into the vet office. Every time we go to the vet at least 3 other pet parents (and staff) ask where I got the carriers because they have never seen one like it. They are sturdy (once one end is zipped) and there are lots of little places they can see out of. HOWEVER. SOMEONE does not like traveling and managed to get out of the zipped carrier in the back seat. At least now I know it's a good idea to use the little collar leash inside it so even if he does get it open, he can't go far.