I have to say that in my case these were just the perfect solution! Since I bought them recently, I don't know what the issue with the tabs was, but they work just fine these days.
Here's the background...
I have a 19 year old kitty who is the love of my life (I know, can you say "cat lady?") and he recently became completely blind. :( While he doesn't suffer from incontinence, the place is relatively large and he often can't find his way to the box. So, after going around in circles or zigzagging the room for a while, he will finally just pee.
After the second time I saw this happen, I decided that I needed to try something quickly. I had originally purchased these about 9 months ago, for a diabetic cat I had who passed on last year. That cat wouldn't let me even try to get the diapers on him. He would fight and scream, you would think I was trying to kill him! But my little angel (I know, more cat lady talk...), being the adorable creature he is, lets me put these on him and it's been just wonderful.
He still circles the room a few times because I just can't convince him that it's ok to do it wherever he is, but he has been using diapers 24/7 and they work great. I usually change him a couple of times a day or so, one pack with 12 lasts about a week. The only thing is that it can be a little messy sometimes when solid things aren't quite as solid as they should be (if you get what I mean...), but I use these combined with pet wipes (that will become baby wipes once I finish the pack I am currently using, since he no longer grooms himself and I know he won't lick the chemicals) and it works just fine.
So, if you have a kitty and wonder if these would work, my certified cat lady opinion is that you'll be fine with these if your kitty allows you to put them on and doesn't remove them. I'd say an old cat who no longer grooms him/herself would probably be fine with it.
By the way, my kitty is very skinny due to his age, and he was a pretty normal average size for a cat (remember the cat in Pet Cemetary? That's what he looks like). If your cat is larger, you should definitely get a larger size or two. I haven't seen the small diapers, but from the size of the medium ones, I would think they are very, very tiny.