Look at it this way, 30$ is 15 rolls when bought per roll.
I guess it is like getting 5 rolls free at that rate if you don't count any of the loading costs and if you can get cartridges for free (what about caps?). If I even used the cheapest Arista non-dx coded cartridges, they would run $.63 each, which eats into $.50 per roll savings (from my previous example) pretty quick unless you re-use them a whole bunch of times. I'd be afraid that the felt would get dirty pretty quickly and I would rather chuck them sooner than later to avoid scratching my film.
I do see where it would be a huge advantage of using custom length rolls for different processing.

) takes a thick plastic card with notches cut down the middle and tapes the film to it. The caps are not pulled off the cassette. This card with the cassettes dangling from the card via tape is then inderted into the film processor and the light-tight door is shut. The gears in the maching grab the notches and pull the film thrall the chems. When it reaches the end, the film is cut off. Most labs just throw away the cassettes, although some do recycle, but both are happy to give them away.
