I have three sets of Flipper Fidelity speakers in my IM, TFLE, and STTNG. I'm very happy with them all. In addition to the speakers, wiring, volume knob, and crossover; for the Sterns (and I think the STTNG) there are wood adapters that go between the speaker panel and new speaker to allow for spacing on the larger speaker that allow you to keep the stock look.
I think it's key to remember that ANY speaker upgrade would be beneficial to the cheap chinese speakers shipped with the game. But the crossover and volume adjustment allow you to fine tune the game to how you like.
And yes, you're paying for the convenience factor too, but it's worth it IMO.
Chris