I've asked various fishermen whom have used both the orvis cassette system and Clearwater reel w/separate spools. The advice they all gave me was to avoid the cassette system and stick with individual spools. The Clearwater large arbor spools are really easy to swap out, and much more durable. I think it's one of those "you get what you pay for" deals.
I followed their advice and have 3 different setups for my 7wt I use for bass fishing: floating line, intermediate sink tip, and sinking line. Honestly the sinking line hardly gets any attention and the other two get all the love depending if I'm throwing poppers or stripping streamers.
If price is the main concern for why you're considering the cassette system vs individual spools, I'm not sure you should be considering either. You're going to have N times the number of spools or cassettes to fill with line either way - not cheap. I would instead just get the standard Clearwater reel with the included single spool and a nice floating or intermediate sink tip depending of the type of water and flies you like to throw. Then save up for another spool & line for a good goal in the future when you are ready and can afford it.
