I bought three different Slatkin & Co. Scentportables at Bath and Body Works for US$5 each during the Semi-Annual Sale and I don't know that they're available at any other store. I've tried one so far- Pineapple Mango- but the other scents are Fresh Linen, Vanilla Coconut, and Cinnamon & Clove Buds. I didn't smell too much mango coming from this Scentportable, but there was plenty of sweet, fake, candy-like pineapple coming from it. It was especially strong the first week, even though the weather was very hot and humid. I open the windows for a few minutes after I start the car to get all the hot air out, and when I'd shut the windows, I could still smell the Scentportable. I'd say this really only lasted maybe three weeks, though. If you're having important guests in your car and need a scent, I'd start using this a week before they were going to be in your car because it can be strongly fragranced at first. And I'd find some place to clip it where your guests couldn't see it, because...
The first thing you need to know about these Scentportables is that they come in a hideous round white plastic container. The only thing that gives them step above the regular scent disks you peel and stick in stinky areas would be the quality of the plastic, the fact that the top is slightly open to you can see the gel, and the clip on the back. But it's still pretty unattractive. At least the clip isn't so strong that it left heavy lines on my car's visor. You could lay the Scentportable flat on the back of the clip and it won't move much, which is good if you're putting it in an area where you can't clip it to something.
To use a Scentportable, you pry off the top cover (not too difficult), peel off the seal on the gel scent disk, the put the cover back on. That's it. They aren't refillable, and you throw them away when you're done. They aren't very environmentally friendly. I still see some gel after the scent wore off, too, so don't expect that you'll need to pitch it only after the gel dries up. I wouldn't repurchase the Pineapple Mango scent, but I'm hoping Vanilla Coconut and Cinnamon & Clove Buds will smell better.
ETA: Cinnamon & Clove Buds is TERRIBLE! It smells like the residual cloud left over in the air after a bunch of Black Cat fireworks are set off. My husband didn't agree that it smells like gunpowder (he's the fireworks expert in this household) but he was also unimpressed with this Scentportable. Thankfully it didn't have much sillage, so you could barely smell it unless you sniffed close to the Scentportable itself, but this particular fragrance was a DEFINITE DUD. I wouldn't purchase it again because I can barely smell it, and because the scent itself is awful in my opinion.