I just added 2 rods and 2 reels and a demo to the shopping cart and its still 20 shipping. 20 is what they charge to IL. So if you were already buying something then the reel demos are free. And you can demo 4 reels at a time to help make up your mind. Thats more ethical than trying them out at bps and returning them and sticking someone with a used reel.
Edit- theres more reels for demo, just search through the site and theres a demo link on each reels page.
How long can you keep them? If you are going to return the reel, don't forget about adding the cost of line. I suppose you could just swap it to another reel but it gets to be a hassle. If you are using FC, it'll cost you $7 or more to spool up assuming you do it yourself. A lot cheaper if you using mono.
Now if you are going on fishing vacation and want to have another premium combo for the trip, this sounds like a good idea. If you use it to your advantage, it is almost like you are renting a rod or reel. Interesting idea.