Perhaps it's a little expensive, but I believe "plum" here is not just a random word, but is referring to the quality of the goods being rented.
Now, one may separately question whether there is anybody in the target market, who wants these clothes but won't drop the funds to just buy them, but I can't speak to that either way; my family is more the "$5 for the all-the-clothes-you-can-stuff-into-a-garbage-bag special" sort of family. No rental service can compete in that part of the market, as fixed costs to ship one box would eat half my wardrobe "budget".