I used them on my cats when I got married & moved in with my husband & his nice furniture (my furniture had been shredded by my cats, and he wanted to keep his furniture in good shape). I'm really thankful that they were available as an option, because they saved my relationship - DH really wouldn't have been happy living with ratty furniture, but there was no way I'd ever consider declawing my babies.
The cats were 9, 9, and 15 years old when I tried the softpaws on them. Only one of the cats (one of the 9-year-olds) really minded having them on, and she's a bit of an obsessive groomer. I used a dab of bitter apple spray on her nail caps before I put them on, and spent some time distracting her with pets, food, and play afterward so the glue had plenty of time to dry. She pulled them off a few times, but I just kept putting them on, and she got used to them after a while. The other cats adjusted to them pretty quickly.
They effectively prevented my cats from damaging the furniture while I taught them which surfaces were OK to scratch on, and which ones were off-limits. After a few months I was able to discontinue using the nail caps, and just went to keeping the cats' nails trimmed short.
The caps lasted about 2 months on the two cats who didn't pull them off, and about 4-6 weeks on the cat who pulled on them. They usually fall off naturally after about 6-8 weeks when the nail is shed, but if they don't fall off and the nail continues to grow out, you can trim off the end of the cap and pull the cap off the nail yourself.
If you're nervous about using them at home the first time, you can call around to vets & groomers in your area to find someone who will apply them for you, and show you how it's done. That's what I did - the vet put them on one of my cats the first time to show me how, so I could do the other cats at home. I found it easier to start with the clear caps to see how much glue I was using, and then I went to using the colored so I could find them more easily if they fell off (plus they look neat).
web site has a nice FAQ section and instruction section, and you can email them if you have questions.
You can usually find softpaws at some vet clinics and grooming shops, at Petsmart and Petco (I've only seen clear caps there), or online from the manufacturer, or on Ebay. You may find some that are called soft claws - don't worry, they're exactly the same thing, just with a different name.
Hope this helps
BTW, the medium size of nail caps fit all of my cats, from 7-lb Felixia to 15-lb Mr. Underfoot. One of Mr's claws might have done better in the large size (the medium was OK but didn't cover as well as a large size might have), but the other 9 claws fit in the medium just fine.