I've used them, and they worked very well for me.
I'm glad you're interested in trying them. I used them for several months while the cats learned to scratch a heavy rag throw rug instead of the carpet & new furniture. But for determined scratchers, you can certainly continue use for however long you need to.
You can find detailed application instructions on www.softpaws.com
If you've never tried them before, you might want to call around to find a groomer or vet who can apply them for you the first time, and ask them to let you watch while they do it - my vet's assistant showed me how to put them on my cats the first time. Also, I'd recommend using the clear ones at least at first, so you can see how much glue you're using. Then, after you've had some practice, you can use the cool colored ones - they're nice because you can easily spot it if your cat has lost one.
Out of the 3 cats I used them on, only one was bad about pulling them off. It helps if you distract the cat for a little while after you've applied the caps - I feed them a can of food & play with them with the laser pointer for a little while. For the cat who was a little more persistent about removing the caps, I just started appying bitter apple (a gel or spray taste deterrent you can find at the pet store) to the caps immediately after I put them on her.
The caps will usually last from 4-8 weeks, depending on how fast your cats' claws grow. They'll fall off as the nail sheath sheds naturally, or as your cat pulls them off. If you notice that a claw is getting pretty long & the cap hasn't come off (my elderly kitty sometimes had this happen), you can clip off the tip of the cap with cat nail trimmers & gently remove it.
Just another thought - even with Softpaws on your cat, I'd recommend against buying carpeting with a loop style - we bought a nice Olefin looped carpet for our living room and the cats & dogs pulled a lot
of snags in that carpet in a matter of days.
I suspect that if large dogs can pull snags in a looped carpet, cats probably can even with Softpaws on.